info201.github.io/data-frames.html at master · info201/info201.github.io · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" lang="" xml:lang="">
<head>

  <meta charset="utf-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge" />
  <title>Chapter 9 Data Frames | Technical Foundations of Informatics</title>
  <meta name="description" content="The course reader for INFO 201: Technical Foundations of Informatics." />
  <meta name="generator" content="bookdown 0.13 and GitBook 2.6.7" />

  <meta property="og:title" content="Chapter 9 Data Frames | Technical Foundations of Informatics" />
  <meta property="og:type" content="book" />
  <meta property="og:url" content="https://info201.github.io/" />
  <meta property="og:image" content="https://info201.github.io/img/cover-img.png" />
  <meta property="og:description" content="The course reader for INFO 201: Technical Foundations of Informatics." />
  <meta name="github-repo" content="info201/book" />

  <meta name="twitter:card" content="summary" />
  <meta name="twitter:title" content="Chapter 9 Data Frames | Technical Foundations of Informatics" />

  <meta name="twitter:description" content="The course reader for INFO 201: Technical Foundations of Informatics." />
  <meta name="twitter:image" content="https://info201.github.io/img/cover-img.png" />

<meta name="author" content="Michael Freeman and Joel Ross" />


<meta name="date" content="2019-09-11" />

  <meta name="viewport" content="width=device-width, initial-scale=1" />
  <meta name="apple-mobile-web-app-capable" content="yes" />
  <meta name="apple-mobile-web-app-status-bar-style" content="black" />

  <link rel="shortcut icon" href="img/favicon.png" type="image/x-icon" />
<link rel="prev" href="lists.html"/>
<link rel="next" href="dplyr.html"/>
<script src="libs/jquery-2.2.3/jquery.min.js"></script>
<link href="libs/gitbook-2.6.7/css/style.css" rel="stylesheet" />
<link href="libs/gitbook-2.6.7/css/plugin-table.css" rel="stylesheet" />
<link href="libs/gitbook-2.6.7/css/plugin-bookdown.css" rel="stylesheet" />
<link href="libs/gitbook-2.6.7/css/plugin-highlight.css" rel="stylesheet" />
<link href="libs/gitbook-2.6.7/css/plugin-search.css" rel="stylesheet" />
<link href="libs/gitbook-2.6.7/css/plugin-fontsettings.css" rel="stylesheet" />


<script>
  (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
  (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
  m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
  })(window,document,'script','https://www.google-analytics.com/analytics.js','ga');

  ga('create', 'UA-98444716-2', 'auto');
  ga('send', 'pageview');

</script>


<style type="text/css">
a.sourceLine { display: inline-block; line-height: 1.25; }
a.sourceLine { pointer-events: none; color: inherit; text-decoration: inherit; }
a.sourceLine:empty { height: 1.2em; }
.sourceCode { overflow: visible; }
code.sourceCode { white-space: pre; position: relative; }
pre.sourceCode { margin: 0; }
@media screen {
div.sourceCode { overflow: auto; }
}
@media print {
code.sourceCode { white-space: pre-wrap; }
a.sourceLine { text-indent: -1em; padding-left: 1em; }
}
pre.numberSource a.sourceLine
  { position: relative; left: -4em; }
pre.numberSource a.sourceLine::before
  { content: attr(data-line-number);
    position: relative; left: -1em; text-align: right; vertical-align: baseline;
    border: none; pointer-events: all; display: inline-block;
    -webkit-touch-callout: none; -webkit-user-select: none;
    -khtml-user-select: none; -moz-user-select: none;
    -ms-user-select: none; user-select: none;
    padding: 0 4px; width: 4em;
    color: #aaaaaa;
  }
pre.numberSource { margin-left: 3em; border-left: 1px solid #aaaaaa;  padding-left: 4px; }
div.sourceCode
  {  }
@media screen {
a.sourceLine::before { text-decoration: underline; }
}
code span.al { color: #ff0000; font-weight: bold; } /* Alert */
code span.an { color: #60a0b0; font-weight: bold; font-style: italic; } /* Annotation */
code span.at { color: #7d9029; } /* Attribute */
code span.bn { color: #40a070; } /* BaseN */
code span.bu { } /* BuiltIn */
code span.cf { color: #007020; font-weight: bold; } /* ControlFlow */
code span.ch { color: #4070a0; } /* Char */
code span.cn { color: #880000; } /* Constant */
code span.co { color: #60a0b0; font-style: italic; } /* Comment */
code span.cv { color: #60a0b0; font-weight: bold; font-style: italic; } /* CommentVar */
code span.do { color: #ba2121; font-style: italic; } /* Documentation */
code span.dt { color: #902000; } /* DataType */
code span.dv { color: #40a070; } /* DecVal */
code span.er { color: #ff0000; font-weight: bold; } /* Error */
code span.ex { } /* Extension */
code span.fl { color: #40a070; } /* Float */
code span.fu { color: #06287e; } /* Function */
code span.im { } /* Import */
code span.in { color: #60a0b0; font-weight: bold; font-style: italic; } /* Information */
code span.kw { color: #007020; font-weight: bold; } /* Keyword */
code span.op { color: #666666; } /* Operator */
code span.ot { color: #007020; } /* Other */
code span.pp { color: #bc7a00; } /* Preprocessor */
code span.sc { color: #4070a0; } /* SpecialChar */
code span.ss { color: #bb6688; } /* SpecialString */
code span.st { color: #4070a0; } /* String */
code span.va { color: #19177c; } /* Variable */
code span.vs { color: #4070a0; } /* VerbatimString */
code span.wa { color: #60a0b0; font-weight: bold; font-style: italic; } /* Warning */
</style>

<link rel="stylesheet" href="css/style.css" type="text/css" />
</head>

<body>


  <div class="book without-animation with-summary font-size-2 font-family-1" data-basepath=".">

    <div class="book-summary">
      <nav role="navigation">

<ul class="summary">
<li><a href="./">Technical Foundations of Informatics</a></li>

<li class="divider"></li>
<li class="chapter" data-level="" data-path="index.html"><a href="index.html"><i class="fa fa-check"></i>About the Book</a></li>
<li class="chapter" data-level="1" data-path="setup-machine.html"><a href="setup-machine.html"><i class="fa fa-check"></i><b>1</b> Setting up your Machine</a><ul>
<li class="chapter" data-level="1.1" data-path="setup-machine.html"><a href="setup-machine.html#git"><i class="fa fa-check"></i><b>1.1</b> Git</a><ul>
<li class="chapter" data-level="1.1.1" data-path="setup-machine.html"><a href="setup-machine.html#github"><i class="fa fa-check"></i><b>1.1.1</b> GitHub</a></li>
</ul></li>
<li class="chapter" data-level="1.2" data-path="setup-machine.html"><a href="setup-machine.html#command-line-tools-bash"><i class="fa fa-check"></i><b>1.2</b> Command-line Tools (Bash)</a><ul>
<li class="chapter" data-level="1.2.1" data-path="setup-machine.html"><a href="setup-machine.html#command-line-on-a-mac"><i class="fa fa-check"></i><b>1.2.1</b> Command-line on a Mac</a></li>
<li class="chapter" data-level="1.2.2" data-path="setup-machine.html"><a href="setup-machine.html#command-line-on-windows"><i class="fa fa-check"></i><b>1.2.2</b> Command-line on Windows</a></li>
</ul></li>
<li class="chapter" data-level="1.3" data-path="setup-machine.html"><a href="setup-machine.html#text-editors"><i class="fa fa-check"></i><b>1.3</b> Text Editors</a><ul>
<li class="chapter" data-level="1.3.1" data-path="setup-machine.html"><a href="setup-machine.html#atom"><i class="fa fa-check"></i><b>1.3.1</b> Atom</a></li>
<li class="chapter" data-level="1.3.2" data-path="setup-machine.html"><a href="setup-machine.html#visual-studio-code"><i class="fa fa-check"></i><b>1.3.2</b> Visual Studio Code</a></li>
<li class="chapter" data-level="1.3.3" data-path="setup-machine.html"><a href="setup-machine.html#sublime-text"><i class="fa fa-check"></i><b>1.3.3</b> Sublime Text</a></li>
</ul></li>
<li class="chapter" data-level="1.4" data-path="setup-machine.html"><a href="setup-machine.html#r-language"><i class="fa fa-check"></i><b>1.4</b> R Language</a></li>
<li class="chapter" data-level="1.5" data-path="setup-machine.html"><a href="setup-machine.html#rstudio"><i class="fa fa-check"></i><b>1.5</b> RStudio</a></li>
<li class="chapter" data-level="" data-path="setup-machine.html"><a href="setup-machine.html#resources"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="chapter" data-level="2" data-path="command-line.html"><a href="command-line.html"><i class="fa fa-check"></i><b>2</b> The Command Line</a><ul>
<li class="chapter" data-level="2.1" data-path="command-line.html"><a href="command-line.html#accessing-the-command-line"><i class="fa fa-check"></i><b>2.1</b> Accessing the Command-Line</a></li>
<li class="chapter" data-level="2.2" data-path="command-line.html"><a href="command-line.html#navigating-the-command-line"><i class="fa fa-check"></i><b>2.2</b> Navigating the Command Line</a><ul>
<li class="chapter" data-level="2.2.1" data-path="command-line.html"><a href="command-line.html#changing-directories"><i class="fa fa-check"></i><b>2.2.1</b> Changing Directories</a></li>
<li class="chapter" data-level="2.2.2" data-path="command-line.html"><a href="command-line.html#listing-files"><i class="fa fa-check"></i><b>2.2.2</b> Listing Files</a></li>
<li class="chapter" data-level="2.2.3" data-path="command-line.html"><a href="command-line.html#paths"><i class="fa fa-check"></i><b>2.2.3</b> Paths</a></li>
</ul></li>
<li class="chapter" data-level="2.3" data-path="command-line.html"><a href="command-line.html#file-commands"><i class="fa fa-check"></i><b>2.3</b> File Commands</a><ul>
<li class="chapter" data-level="2.3.1" data-path="command-line.html"><a href="command-line.html#learning-new-commands"><i class="fa fa-check"></i><b>2.3.1</b> Learning New Commands</a></li>
</ul></li>
<li class="chapter" data-level="2.4" data-path="command-line.html"><a href="command-line.html#dealing-with-errors"><i class="fa fa-check"></i><b>2.4</b> Dealing With Errors</a></li>
<li class="chapter" data-level="" data-path="command-line.html"><a href="command-line.html#resources-1"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="chapter" data-level="3" data-path="markdown.html"><a href="markdown.html"><i class="fa fa-check"></i><b>3</b> Markdown</a><ul>
<li class="chapter" data-level="3.1" data-path="markdown.html"><a href="markdown.html#writing-markdown"><i class="fa fa-check"></i><b>3.1</b> Writing Markdown</a><ul>
<li class="chapter" data-level="3.1.1" data-path="markdown.html"><a href="markdown.html#text-formatting"><i class="fa fa-check"></i><b>3.1.1</b> Text Formatting</a></li>
<li class="chapter" data-level="3.1.2" data-path="markdown.html"><a href="markdown.html#text-blocks"><i class="fa fa-check"></i><b>3.1.2</b> Text Blocks</a></li>
</ul></li>
<li class="chapter" data-level="3.2" data-path="markdown.html"><a href="markdown.html#rendering-markdown"><i class="fa fa-check"></i><b>3.2</b> Rendering Markdown</a></li>
<li class="chapter" data-level="" data-path="markdown.html"><a href="markdown.html#resources-2"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="chapter" data-level="4" data-path="git-basics.html"><a href="git-basics.html"><i class="fa fa-check"></i><b>4</b> Git and GitHub</a><ul>
<li class="chapter" data-level="4.1" data-path="git-basics.html"><a href="git-basics.html#what-is-this-git-thing-anyway"><i class="fa fa-check"></i><b>4.1</b> What is this <em>git</em> thing anyway?</a><ul>
<li class="chapter" data-level="4.1.1" data-path="git-basics.html"><a href="git-basics.html#git-core-concepts"><i class="fa fa-check"></i><b>4.1.1</b> Git Core Concepts</a></li>
<li class="chapter" data-level="4.1.2" data-path="git-basics.html"><a href="git-basics.html#wait-but-what-is-github-then"><i class="fa fa-check"></i><b>4.1.2</b> Wait, but what is GitHub then?</a></li>
</ul></li>
<li class="chapter" data-level="4.2" data-path="git-basics.html"><a href="git-basics.html#installation-setup"><i class="fa fa-check"></i><b>4.2</b> Installation &amp; Setup</a><ul>
<li class="chapter" data-level="4.2.1" data-path="git-basics.html"><a href="git-basics.html#creating-a-repo"><i class="fa fa-check"></i><b>4.2.1</b> Creating a Repo</a></li>
<li class="chapter" data-level="4.2.2" data-path="git-basics.html"><a href="git-basics.html#checking-status"><i class="fa fa-check"></i><b>4.2.2</b> Checking Status</a></li>
</ul></li>
<li class="chapter" data-level="4.3" data-path="git-basics.html"><a href="git-basics.html#making-changes"><i class="fa fa-check"></i><b>4.3</b> Making Changes</a><ul>
<li class="chapter" data-level="4.3.1" data-path="git-basics.html"><a href="git-basics.html#adding-files"><i class="fa fa-check"></i><b>4.3.1</b> Adding Files</a></li>
<li class="chapter" data-level="4.3.2" data-path="git-basics.html"><a href="git-basics.html#committing"><i class="fa fa-check"></i><b>4.3.2</b> Committing</a></li>
<li class="chapter" data-level="4.3.3" data-path="git-basics.html"><a href="git-basics.html#commit-history"><i class="fa fa-check"></i><b>4.3.3</b> Commit History</a></li>
<li class="chapter" data-level="4.3.4" data-path="git-basics.html"><a href="git-basics.html#reviewing-the-process"><i class="fa fa-check"></i><b>4.3.4</b> Reviewing the Process</a></li>
<li class="chapter" data-level="4.3.5" data-path="git-basics.html"><a href="git-basics.html#gitignore"><i class="fa fa-check"></i><b>4.3.5</b> The <code>.gitignore</code> File</a></li>
</ul></li>
<li class="chapter" data-level="4.4" data-path="git-basics.html"><a href="git-basics.html#github-and-remotes"><i class="fa fa-check"></i><b>4.4</b> GitHub and Remotes</a><ul>
<li class="chapter" data-level="4.4.1" data-path="git-basics.html"><a href="git-basics.html#forking-and-cloning"><i class="fa fa-check"></i><b>4.4.1</b> Forking and Cloning</a></li>
<li class="chapter" data-level="4.4.2" data-path="git-basics.html"><a href="git-basics.html#pushing-and-pulling"><i class="fa fa-check"></i><b>4.4.2</b> Pushing and Pulling</a></li>
<li class="chapter" data-level="4.4.3" data-path="git-basics.html"><a href="git-basics.html#reviewing-the-process-1"><i class="fa fa-check"></i><b>4.4.3</b> Reviewing The Process</a></li>
</ul></li>
<li class="chapter" data-level="4.5" data-path="git-basics.html"><a href="git-basics.html#course-assignments-on-github"><i class="fa fa-check"></i><b>4.5</b> Course Assignments on GitHub</a></li>
<li class="chapter" data-level="4.6" data-path="git-basics.html"><a href="git-basics.html#command-summary"><i class="fa fa-check"></i><b>4.6</b> Command Summary</a></li>
<li class="chapter" data-level="" data-path="git-basics.html"><a href="git-basics.html#resources-3"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="chapter" data-level="5" data-path="r-intro.html"><a href="r-intro.html"><i class="fa fa-check"></i><b>5</b> Introduction to R</a><ul>
<li class="chapter" data-level="5.1" data-path="r-intro.html"><a href="r-intro.html#programming-with-r"><i class="fa fa-check"></i><b>5.1</b> Programming with R</a></li>
<li class="chapter" data-level="5.2" data-path="r-intro.html"><a href="r-intro.html#running-r-scripts"><i class="fa fa-check"></i><b>5.2</b> Running R Scripts</a><ul>
<li class="chapter" data-level="5.2.1" data-path="r-intro.html"><a href="r-intro.html#running-r-cmd"><i class="fa fa-check"></i><b>5.2.1</b> Command-Line</a></li>
<li class="chapter" data-level="5.2.2" data-path="r-intro.html"><a href="r-intro.html#running-r-rstudio"><i class="fa fa-check"></i><b>5.2.2</b> RStudio</a></li>
</ul></li>
<li class="chapter" data-level="5.3" data-path="r-intro.html"><a href="r-intro.html#comments"><i class="fa fa-check"></i><b>5.3</b> Comments</a></li>
<li class="chapter" data-level="5.4" data-path="r-intro.html"><a href="r-intro.html#variables"><i class="fa fa-check"></i><b>5.4</b> Variables</a><ul>
<li class="chapter" data-level="5.4.1" data-path="r-intro.html"><a href="r-intro.html#basic-data-types"><i class="fa fa-check"></i><b>5.4.1</b> Basic Data Types</a></li>
</ul></li>
<li class="chapter" data-level="5.5" data-path="r-intro.html"><a href="r-intro.html#gettinghelp"><i class="fa fa-check"></i><b>5.5</b> Getting Help</a></li>
<li class="chapter" data-level="" data-path="r-intro.html"><a href="r-intro.html#resources-4"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="chapter" data-level="6" data-path="functions.html"><a href="functions.html"><i class="fa fa-check"></i><b>6</b> Functions</a><ul>
<li class="chapter" data-level="6.1" data-path="functions.html"><a href="functions.html#what-are-functions"><i class="fa fa-check"></i><b>6.1</b> What are Functions?</a></li>
<li class="chapter" data-level="6.2" data-path="functions.html"><a href="functions.html#how-to-use-functions"><i class="fa fa-check"></i><b>6.2</b> How to Use Functions</a></li>
<li class="chapter" data-level="6.3" data-path="functions.html"><a href="functions.html#built-in-r-functions"><i class="fa fa-check"></i><b>6.3</b> Built-in R Functions</a></li>
<li class="chapter" data-level="6.4" data-path="functions.html"><a href="functions.html#loading-functions"><i class="fa fa-check"></i><b>6.4</b> Loading Functions</a></li>
<li class="chapter" data-level="6.5" data-path="functions.html"><a href="functions.html#writing-functions"><i class="fa fa-check"></i><b>6.5</b> Writing Functions</a></li>
<li class="chapter" data-level="6.6" data-path="functions.html"><a href="functions.html#conditional-statements"><i class="fa fa-check"></i><b>6.6</b> Conditional Statements</a></li>
<li class="chapter" data-level="" data-path="functions.html"><a href="functions.html#resources-5"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="chapter" data-level="7" data-path="vectors.html"><a href="vectors.html"><i class="fa fa-check"></i><b>7</b> Vectors</a><ul>
<li class="chapter" data-level="7.1" data-path="vectors.html"><a href="vectors.html#what-is-a-vector"><i class="fa fa-check"></i><b>7.1</b> What is a Vector?</a></li>
<li class="chapter" data-level="7.2" data-path="vectors.html"><a href="vectors.html#creating-vectors"><i class="fa fa-check"></i><b>7.2</b> Creating Vectors</a></li>
<li class="chapter" data-level="7.3" data-path="vectors.html"><a href="vectors.html#vector-indices"><i class="fa fa-check"></i><b>7.3</b> Vector Indices</a><ul>
<li class="chapter" data-level="7.3.1" data-path="vectors.html"><a href="vectors.html#simple-numeric-indices"><i class="fa fa-check"></i><b>7.3.1</b> Simple Numeric Indices</a></li>
<li class="chapter" data-level="7.3.2" data-path="vectors.html"><a href="vectors.html#multiple-indices"><i class="fa fa-check"></i><b>7.3.2</b> Multiple Indices</a></li>
<li class="chapter" data-level="7.3.3" data-path="vectors.html"><a href="vectors.html#logical-indexing"><i class="fa fa-check"></i><b>7.3.3</b> Logical Indexing</a></li>
<li class="chapter" data-level="7.3.4" data-path="vectors.html"><a href="vectors.html#named-vectors-and-character-indexing"><i class="fa fa-check"></i><b>7.3.4</b> Named Vectors and Character Indexing</a></li>
</ul></li>
<li class="chapter" data-level="7.4" data-path="vectors.html"><a href="vectors.html#modifying-vectors"><i class="fa fa-check"></i><b>7.4</b> Modifying Vectors</a></li>
<li class="chapter" data-level="7.5" data-path="vectors.html"><a href="vectors.html#vectorized-operations"><i class="fa fa-check"></i><b>7.5</b> Vectorized Operations</a><ul>
<li class="chapter" data-level="7.5.1" data-path="vectors.html"><a href="vectors.html#vectorized-operators"><i class="fa fa-check"></i><b>7.5.1</b> Vectorized Operators</a></li>
<li class="chapter" data-level="7.5.2" data-path="vectors.html"><a href="vectors.html#vectorized-functions"><i class="fa fa-check"></i><b>7.5.2</b> Vectorized Functions</a></li>
<li class="chapter" data-level="7.5.3" data-path="vectors.html"><a href="vectors.html#recycling"><i class="fa fa-check"></i><b>7.5.3</b> Recycling</a></li>
<li class="chapter" data-level="7.5.4" data-path="vectors.html"><a href="vectors.html#r-is-a-vectorized-world"><i class="fa fa-check"></i><b>7.5.4</b> R Is a Vectorized World</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="vectors.html"><a href="vectors.html#resources-6"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="chapter" data-level="8" data-path="lists.html"><a href="lists.html"><i class="fa fa-check"></i><b>8</b> Lists</a><ul>
<li class="chapter" data-level="8.1" data-path="lists.html"><a href="lists.html#what-is-a-list"><i class="fa fa-check"></i><b>8.1</b> What is a List?</a></li>
<li class="chapter" data-level="8.2" data-path="lists.html"><a href="lists.html#creating-lists"><i class="fa fa-check"></i><b>8.2</b> Creating Lists</a></li>
<li class="chapter" data-level="8.3" data-path="lists.html"><a href="lists.html#accessing-list-elements"><i class="fa fa-check"></i><b>8.3</b> Accessing List Elements</a><ul>
<li class="chapter" data-level="8.3.1" data-path="lists.html"><a href="lists.html#lists-indexing-by-position"><i class="fa fa-check"></i><b>8.3.1</b> Indexing by position</a></li>
<li class="chapter" data-level="8.3.2" data-path="lists.html"><a href="lists.html#indexing-by-name"><i class="fa fa-check"></i><b>8.3.2</b> Indexing by Name</a></li>
<li class="chapter" data-level="8.3.3" data-path="lists.html"><a href="lists.html#indexing-by-logical-vector"><i class="fa fa-check"></i><b>8.3.3</b> Indexing by Logical Vector</a></li>
<li class="chapter" data-level="8.3.4" data-path="lists.html"><a href="lists.html#lists-dollar-shortcut"><i class="fa fa-check"></i><b>8.3.4</b> Extracting named elements with <code>$</code></a></li>
<li class="chapter" data-level="8.3.5" data-path="lists.html"><a href="lists.html#single-vs.double-brackets-vs.dollar"><i class="fa fa-check"></i><b>8.3.5</b> Single vs. Double Brackets vs. Dollar</a></li>
</ul></li>
<li class="chapter" data-level="8.4" data-path="lists.html"><a href="lists.html#modifying-lists"><i class="fa fa-check"></i><b>8.4</b> Modifying Lists</a></li>
<li class="chapter" data-level="8.5" data-path="lists.html"><a href="lists.html#the-lapply-function"><i class="fa fa-check"></i><b>8.5</b> The <code>lapply()</code> Function</a></li>
<li class="chapter" data-level="" data-path="lists.html"><a href="lists.html#resources-7"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="chapter" data-level="9" data-path="data-frames.html"><a href="data-frames.html"><i class="fa fa-check"></i><b>9</b> Data Frames</a><ul>
<li class="chapter" data-level="9.1" data-path="data-frames.html"><a href="data-frames.html#what-is-a-data-frame"><i class="fa fa-check"></i><b>9.1</b> What is a Data Frame?</a><ul>
<li class="chapter" data-level="9.1.1" data-path="data-frames.html"><a href="data-frames.html#creating-data-frames"><i class="fa fa-check"></i><b>9.1.1</b> Creating Data Frames</a></li>
<li class="chapter" data-level="9.1.2" data-path="data-frames.html"><a href="data-frames.html#describing-structure-of-data-frames"><i class="fa fa-check"></i><b>9.1.2</b> Describing Structure of Data Frames</a></li>
<li class="chapter" data-level="9.1.3" data-path="data-frames.html"><a href="data-frames.html#accessing-data-in-data-frames"><i class="fa fa-check"></i><b>9.1.3</b> Accessing Data in Data Frames</a></li>
</ul></li>
<li class="chapter" data-level="9.2" data-path="data-frames.html"><a href="data-frames.html#csv-files"><i class="fa fa-check"></i><b>9.2</b> Working with CSV Data</a><ul>
<li class="chapter" data-level="9.2.1" data-path="data-frames.html"><a href="data-frames.html#working-directory"><i class="fa fa-check"></i><b>9.2.1</b> Working Directory</a></li>
</ul></li>
<li class="chapter" data-level="9.3" data-path="data-frames.html"><a href="data-frames.html#factors"><i class="fa fa-check"></i><b>9.3</b> Factor Variables</a></li>
<li class="chapter" data-level="" data-path="data-frames.html"><a href="data-frames.html#resources-8"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="chapter" data-level="10" data-path="dplyr.html"><a href="dplyr.html"><i class="fa fa-check"></i><b>10</b> The <code>dplyr</code> Library</a><ul>
<li class="chapter" data-level="10.1" data-path="dplyr.html"><a href="dplyr.html#a-grammar-of-data-manipulation"><i class="fa fa-check"></i><b>10.1</b> A Grammar of Data Manipulation</a></li>
<li class="chapter" data-level="10.2" data-path="dplyr.html"><a href="dplyr.html#using-dplyr-functions"><i class="fa fa-check"></i><b>10.2</b> Using <code>dplyr</code> Functions</a><ul>
<li class="chapter" data-level="10.2.1" data-path="dplyr.html"><a href="dplyr.html#select"><i class="fa fa-check"></i><b>10.2.1</b> Select</a></li>
<li class="chapter" data-level="10.2.2" data-path="dplyr.html"><a href="dplyr.html#filter"><i class="fa fa-check"></i><b>10.2.2</b> Filter</a></li>
<li class="chapter" data-level="10.2.3" data-path="dplyr.html"><a href="dplyr.html#mutate"><i class="fa fa-check"></i><b>10.2.3</b> Mutate</a></li>
<li class="chapter" data-level="10.2.4" data-path="dplyr.html"><a href="dplyr.html#arrange"><i class="fa fa-check"></i><b>10.2.4</b> Arrange</a></li>
<li class="chapter" data-level="10.2.5" data-path="dplyr.html"><a href="dplyr.html#summarize"><i class="fa fa-check"></i><b>10.2.5</b> Summarize</a></li>
<li class="chapter" data-level="10.2.6" data-path="dplyr.html"><a href="dplyr.html#distinct"><i class="fa fa-check"></i><b>10.2.6</b> Distinct</a></li>
</ul></li>
<li class="chapter" data-level="10.3" data-path="dplyr.html"><a href="dplyr.html#multiple-operations"><i class="fa fa-check"></i><b>10.3</b> Multiple Operations</a><ul>
<li class="chapter" data-level="10.3.1" data-path="dplyr.html"><a href="dplyr.html#the-pipe-operator"><i class="fa fa-check"></i><b>10.3.1</b> The Pipe Operator</a></li>
</ul></li>
<li class="chapter" data-level="10.4" data-path="dplyr.html"><a href="dplyr.html#grouped-operations"><i class="fa fa-check"></i><b>10.4</b> Grouped Operations</a></li>
<li class="chapter" data-level="10.5" data-path="dplyr.html"><a href="dplyr.html#joins"><i class="fa fa-check"></i><b>10.5</b> Joins</a></li>
<li class="chapter" data-level="10.6" data-path="dplyr.html"><a href="dplyr.html#non-standard-evaluation-vs.standard-evaluation"><i class="fa fa-check"></i><b>10.6</b> Non-Standard Evaluation vs. Standard Evaluation</a><ul>
<li class="chapter" data-level="10.6.1" data-path="dplyr.html"><a href="dplyr.html#explicit-standard-evaluation"><i class="fa fa-check"></i><b>10.6.1</b> Explicit Standard Evaluation</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="dplyr.html"><a href="dplyr.html#resources-9"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="chapter" data-level="11" data-path="apis.html"><a href="apis.html"><i class="fa fa-check"></i><b>11</b> Accessing Web APIs</a><ul>
<li class="chapter" data-level="11.1" data-path="apis.html"><a href="apis.html#what-is-a-web-api"><i class="fa fa-check"></i><b>11.1</b> What is a Web API?</a></li>
<li class="chapter" data-level="11.2" data-path="apis.html"><a href="apis.html#restful-requests"><i class="fa fa-check"></i><b>11.2</b> RESTful Requests</a><ul>
<li class="chapter" data-level="11.2.1" data-path="apis.html"><a href="apis.html#uris"><i class="fa fa-check"></i><b>11.2.1</b> URIs</a></li>
<li class="chapter" data-level="11.2.2" data-path="apis.html"><a href="apis.html#http-verbs"><i class="fa fa-check"></i><b>11.2.2</b> HTTP Verbs</a></li>
</ul></li>
<li class="chapter" data-level="11.3" data-path="apis.html"><a href="apis.html#accessing-web-apis"><i class="fa fa-check"></i><b>11.3</b> Accessing Web APIs</a></li>
<li class="chapter" data-level="11.4" data-path="apis.html"><a href="apis.html#json"><i class="fa fa-check"></i><b>11.4</b> JSON Data</a><ul>
<li class="chapter" data-level="11.4.1" data-path="apis.html"><a href="apis.html#parsing-json"><i class="fa fa-check"></i><b>11.4.1</b> Parsing JSON</a></li>
<li class="chapter" data-level="11.4.2" data-path="apis.html"><a href="apis.html#flattening-data"><i class="fa fa-check"></i><b>11.4.2</b> Flattening Data</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="apis.html"><a href="apis.html#resources-10"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="chapter" data-level="12" data-path="r-markdown.html"><a href="r-markdown.html"><i class="fa fa-check"></i><b>12</b> R Markdown</a><ul>
<li class="chapter" data-level="12.1" data-path="r-markdown.html"><a href="r-markdown.html#r-markdown-and-rstudio"><i class="fa fa-check"></i><b>12.1</b> R Markdown and RStudio</a><ul>
<li class="chapter" data-level="12.1.1" data-path="r-markdown.html"><a href="r-markdown.html#creating-.rmd-files"><i class="fa fa-check"></i><b>12.1.1</b> Creating <code>.Rmd</code> Files</a></li>
<li class="chapter" data-level="12.1.2" data-path="r-markdown.html"><a href="r-markdown.html#rmd-content"><i class="fa fa-check"></i><b>12.1.2</b> <code>.Rmd</code> Content</a></li>
<li class="chapter" data-level="12.1.3" data-path="r-markdown.html"><a href="r-markdown.html#knitting-documents"><i class="fa fa-check"></i><b>12.1.3</b> Knitting Documents</a></li>
<li class="chapter" data-level="12.1.4" data-path="r-markdown.html"><a href="r-markdown.html#html"><i class="fa fa-check"></i><b>12.1.4</b> HTML</a></li>
</ul></li>
<li class="chapter" data-level="12.2" data-path="r-markdown.html"><a href="r-markdown.html#r-markdown-syntax"><i class="fa fa-check"></i><b>12.2</b> R Markdown Syntax</a><ul>
<li class="chapter" data-level="12.2.1" data-path="r-markdown.html"><a href="r-markdown.html#r-code-chunks"><i class="fa fa-check"></i><b>12.2.1</b> R Code Chunks</a></li>
<li class="chapter" data-level="12.2.2" data-path="r-markdown.html"><a href="r-markdown.html#inline-code"><i class="fa fa-check"></i><b>12.2.2</b> Inline Code</a></li>
</ul></li>
<li class="chapter" data-level="12.3" data-path="r-markdown.html"><a href="r-markdown.html#rendering-data"><i class="fa fa-check"></i><b>12.3</b> Rendering Data</a><ul>
<li class="chapter" data-level="12.3.1" data-path="r-markdown.html"><a href="r-markdown.html#rendering-strings"><i class="fa fa-check"></i><b>12.3.1</b> Rendering Strings</a></li>
<li class="chapter" data-level="12.3.2" data-path="r-markdown.html"><a href="r-markdown.html#rendering-lists"><i class="fa fa-check"></i><b>12.3.2</b> Rendering Lists</a></li>
<li class="chapter" data-level="12.3.3" data-path="r-markdown.html"><a href="r-markdown.html#rendering-tables"><i class="fa fa-check"></i><b>12.3.3</b> Rendering Tables</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="r-markdown.html"><a href="r-markdown.html#resources-11"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="chapter" data-level="13" data-path="ggplot2.html"><a href="ggplot2.html"><i class="fa fa-check"></i><b>13</b> The <code>gglot2</code> Library</a><ul>
<li class="chapter" data-level="13.1" data-path="ggplot2.html"><a href="ggplot2.html#a-grammar-of-graphics"><i class="fa fa-check"></i><b>13.1</b> A Grammar of Graphics</a></li>
<li class="chapter" data-level="13.2" data-path="ggplot2.html"><a href="ggplot2.html#basic-plotting-with-ggplot2"><i class="fa fa-check"></i><b>13.2</b> Basic Plotting with <code>ggplot2</code></a><ul>
<li class="chapter" data-level="13.2.1" data-path="ggplot2.html"><a href="ggplot2.html#ggplot2-library"><i class="fa fa-check"></i><b>13.2.1</b> <em>ggplot2</em> library</a></li>
<li class="chapter" data-level="13.2.2" data-path="ggplot2.html"><a href="ggplot2.html#mpg-data"><i class="fa fa-check"></i><b>13.2.2</b> <em>mpg</em> data</a></li>
<li class="chapter" data-level="13.2.3" data-path="ggplot2.html"><a href="ggplot2.html#our-first-ggplot"><i class="fa fa-check"></i><b>13.2.3</b> Our first ggplot</a></li>
<li class="chapter" data-level="13.2.4" data-path="ggplot2.html"><a href="ggplot2.html#aesthetic-mappings"><i class="fa fa-check"></i><b>13.2.4</b> Aesthetic Mappings</a></li>
</ul></li>
<li class="chapter" data-level="13.3" data-path="ggplot2.html"><a href="ggplot2.html#complex-plots"><i class="fa fa-check"></i><b>13.3</b> Complex Plots</a><ul>
<li class="chapter" data-level="13.3.1" data-path="ggplot2.html"><a href="ggplot2.html#specifying-geometry"><i class="fa fa-check"></i><b>13.3.1</b> Specifying Geometry</a></li>
<li class="chapter" data-level="13.3.2" data-path="ggplot2.html"><a href="ggplot2.html#styling-with-scales"><i class="fa fa-check"></i><b>13.3.2</b> Styling with Scales</a></li>
<li class="chapter" data-level="13.3.3" data-path="ggplot2.html"><a href="ggplot2.html#coordinate-systems"><i class="fa fa-check"></i><b>13.3.3</b> Coordinate Systems</a></li>
<li class="chapter" data-level="13.3.4" data-path="ggplot2.html"><a href="ggplot2.html#facets"><i class="fa fa-check"></i><b>13.3.4</b> Facets</a></li>
<li class="chapter" data-level="13.3.5" data-path="ggplot2.html"><a href="ggplot2.html#labels-annotations"><i class="fa fa-check"></i><b>13.3.5</b> Labels &amp; Annotations</a></li>
</ul></li>
<li class="chapter" data-level="13.4" data-path="ggplot2.html"><a href="ggplot2.html#plotting-in-scripts"><i class="fa fa-check"></i><b>13.4</b> Plotting in Scripts</a></li>
<li class="chapter" data-level="13.5" data-path="ggplot2.html"><a href="ggplot2.html#other-visualization-libraries"><i class="fa fa-check"></i><b>13.5</b> Other Visualization Libraries</a></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#resources-12"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="chapter" data-level="14" data-path="git-branches.html"><a href="git-branches.html"><i class="fa fa-check"></i><b>14</b> Git Branches</a><ul>
<li class="chapter" data-level="14.1" data-path="git-branches.html"><a href="git-branches.html#git-branches-1"><i class="fa fa-check"></i><b>14.1</b> Git Branches</a></li>
<li class="chapter" data-level="14.2" data-path="git-branches.html"><a href="git-branches.html#merging"><i class="fa fa-check"></i><b>14.2</b> Merging</a><ul>
<li class="chapter" data-level="14.2.1" data-path="git-branches.html"><a href="git-branches.html#merge-conflicts"><i class="fa fa-check"></i><b>14.2.1</b> Merge Conflicts</a></li>
</ul></li>
<li class="chapter" data-level="14.3" data-path="git-branches.html"><a href="git-branches.html#undoing-changes"><i class="fa fa-check"></i><b>14.3</b> Undoing Changes</a></li>
<li class="chapter" data-level="14.4" data-path="git-branches.html"><a href="git-branches.html#github-and-branches"><i class="fa fa-check"></i><b>14.4</b> GitHub and Branches</a><ul>
<li class="chapter" data-level="14.4.1" data-path="git-branches.html"><a href="git-branches.html#github-pages"><i class="fa fa-check"></i><b>14.4.1</b> GitHub Pages</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="git-branches.html"><a href="git-branches.html#resources-13"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="chapter" data-level="15" data-path="git-collaboration.html"><a href="git-collaboration.html"><i class="fa fa-check"></i><b>15</b> Git Collaboration</a><ul>
<li class="chapter" data-level="15.1" data-path="git-collaboration.html"><a href="git-collaboration.html#centralized-workflow"><i class="fa fa-check"></i><b>15.1</b> Centralized Workflow</a></li>
<li class="chapter" data-level="15.2" data-path="git-collaboration.html"><a href="git-collaboration.html#feature-branch-workflow"><i class="fa fa-check"></i><b>15.2</b> Feature Branch Workflow</a></li>
<li class="chapter" data-level="15.3" data-path="git-collaboration.html"><a href="git-collaboration.html#forking-workflow"><i class="fa fa-check"></i><b>15.3</b> Forking Workflow</a><ul>
<li class="chapter" data-level="15.3.1" data-path="git-collaboration.html"><a href="git-collaboration.html#pull-requests"><i class="fa fa-check"></i><b>15.3.1</b> Pull Requests</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="git-collaboration.html"><a href="git-collaboration.html#resources-14"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="chapter" data-level="16" data-path="shiny.html"><a href="shiny.html"><i class="fa fa-check"></i><b>16</b> The <code>shiny</code> Framework</a><ul>
<li class="chapter" data-level="16.1" data-path="shiny.html"><a href="shiny.html#creating-shiny-apps"><i class="fa fa-check"></i><b>16.1</b> Creating Shiny Apps</a><ul>
<li class="chapter" data-level="16.1.1" data-path="shiny.html"><a href="shiny.html#application-structure"><i class="fa fa-check"></i><b>16.1.1</b> Application Structure</a></li>
<li class="chapter" data-level="16.1.2" data-path="shiny.html"><a href="shiny.html#the-ui"><i class="fa fa-check"></i><b>16.1.2</b> The UI</a></li>
<li class="chapter" data-level="16.1.3" data-path="shiny.html"><a href="shiny.html#the-server"><i class="fa fa-check"></i><b>16.1.3</b> The Server</a></li>
</ul></li>
<li class="chapter" data-level="16.2" data-path="shiny.html"><a href="shiny.html#publishing-shiny-apps"><i class="fa fa-check"></i><b>16.2</b> Publishing Shiny Apps</a></li>
<li class="chapter" data-level="" data-path="shiny.html"><a href="shiny.html#resources-15"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="appendix"><span><b>Special Topics</b></span></li>
<li class="chapter" data-level="A" data-path="plotly.html"><a href="plotly.html"><i class="fa fa-check"></i><b>A</b> Plotly</a><ul>
<li class="chapter" data-level="A.1" data-path="plotly.html"><a href="plotly.html#getting-started"><i class="fa fa-check"></i><b>A.1</b> Getting Started</a></li>
<li class="chapter" data-level="A.2" data-path="plotly.html"><a href="plotly.html#basic-charts"><i class="fa fa-check"></i><b>A.2</b> Basic Charts</a></li>
<li class="chapter" data-level="A.3" data-path="plotly.html"><a href="plotly.html#layout"><i class="fa fa-check"></i><b>A.3</b> Layout</a></li>
<li class="chapter" data-level="A.4" data-path="plotly.html"><a href="plotly.html#hovers"><i class="fa fa-check"></i><b>A.4</b> Hovers</a></li>
<li class="chapter" data-level="" data-path="plotly.html"><a href="plotly.html#resources-16"><i class="fa fa-check"></i>Resources</a></li>
</ul></li>
<li class="chapter" data-level="B" data-path="control-structures.html"><a href="control-structures.html"><i class="fa fa-check"></i><b>B</b> R Language Control Structures</a><ul>
<li class="chapter" data-level="B.1" data-path="control-structures.html"><a href="control-structures.html#loops"><i class="fa fa-check"></i><b>B.1</b> Loops</a><ul>
<li class="chapter" data-level="B.1.1" data-path="control-structures.html"><a href="control-structures.html#for-loop"><i class="fa fa-check"></i><b>B.1.1</b> For Loop</a></li>
<li class="chapter" data-level="B.1.2" data-path="control-structures.html"><a href="control-structures.html#while-loop"><i class="fa fa-check"></i><b>B.1.2</b> While-loop</a></li>
<li class="chapter" data-level="B.1.3" data-path="control-structures.html"><a href="control-structures.html#repeat-loop"><i class="fa fa-check"></i><b>B.1.3</b> repeat-loop</a></li>
<li class="chapter" data-level="B.1.4" data-path="control-structures.html"><a href="control-structures.html#leaving-early-break-and-next"><i class="fa fa-check"></i><b>B.1.4</b> Leaving Early: <code>break</code> and <code>next</code></a></li>
<li class="chapter" data-level="B.1.5" data-path="control-structures.html"><a href="control-structures.html#when-not-to-use-loops-in-r"><i class="fa fa-check"></i><b>B.1.5</b> When (Not) To Use Loops In R?</a></li>
</ul></li>
<li class="chapter" data-level="B.2" data-path="control-structures.html"><a href="control-structures.html#more-about-if-and-else"><i class="fa fa-check"></i><b>B.2</b> More about <code>if</code> and <code>else</code></a><ul>
<li class="chapter" data-level="B.2.1" data-path="control-structures.html"><a href="control-structures.html#where-to-put-else"><i class="fa fa-check"></i><b>B.2.1</b> Where To Put Else</a></li>
<li class="chapter" data-level="B.2.2" data-path="control-structures.html"><a href="control-structures.html#return-value"><i class="fa fa-check"></i><b>B.2.2</b> Return Value</a></li>
</ul></li>
<li class="chapter" data-level="B.3" data-path="control-structures.html"><a href="control-structures.html#switch-choosing-between-multiple-conditions"><i class="fa fa-check"></i><b>B.3</b> <code>switch</code>: Choosing Between Multiple Conditions</a></li>
</ul></li>
<li class="chapter" data-level="C" data-path="data-tables.html"><a href="data-tables.html"><i class="fa fa-check"></i><b>C</b> Thinking Big: Data Tables</a><ul>
<li class="chapter" data-level="C.1" data-path="data-tables.html"><a href="data-tables.html#background-passing-by-value-and-passing-by-reference"><i class="fa fa-check"></i><b>C.1</b> Background: Passing By Value And Passing By Reference</a></li>
<li class="chapter" data-level="C.2" data-path="data-tables.html"><a href="data-tables.html#data-tables-introduction"><i class="fa fa-check"></i><b>C.2</b> Data Tables: Introduction</a><ul>
<li class="chapter" data-level="C.2.1" data-path="data-tables.html"><a href="data-tables.html#replacement-for-data-frames-sort-of"><i class="fa fa-check"></i><b>C.2.1</b> Replacement for Data Frames (Sort of)</a></li>
<li class="chapter" data-level="C.2.2" data-path="data-tables.html"><a href="data-tables.html#fast-reading-and-writing"><i class="fa fa-check"></i><b>C.2.2</b> Fast Reading and Writing</a></li>
</ul></li>
<li class="chapter" data-level="C.3" data-path="data-tables.html"><a href="data-tables.html#indexing-the-major-powerhorse-of-data-tables"><i class="fa fa-check"></i><b>C.3</b> Indexing: The Major Powerhorse of Data Tables</a><ul>
<li class="chapter" data-level="C.3.1" data-path="data-tables.html"><a href="data-tables.html#i-select-observations"><i class="fa fa-check"></i><b>C.3.1</b> i: Select Observations</a></li>
<li class="chapter" data-level="C.3.2" data-path="data-tables.html"><a href="data-tables.html#j-work-with-columns"><i class="fa fa-check"></i><b>C.3.2</b> j: Work with Columns</a></li>
<li class="chapter" data-level="C.3.3" data-path="data-tables.html"><a href="data-tables.html#group-in-by"><i class="fa fa-check"></i><b>C.3.3</b> Group in <code>by</code></a></li>
</ul></li>
<li class="chapter" data-level="C.4" data-path="data-tables.html"><a href="data-tables.html#create-variables-by-reference"><i class="fa fa-check"></i><b>C.4</b> <code>:=</code>–Create variables by reference</a></li>
<li class="chapter" data-level="C.5" data-path="data-tables.html"><a href="data-tables.html#keys"><i class="fa fa-check"></i><b>C.5</b> keys</a></li>
<li class="chapter" data-level="C.6" data-path="data-tables.html"><a href="data-tables.html#resources-17"><i class="fa fa-check"></i><b>C.6</b> Resources</a></li>
</ul></li>
<li class="chapter" data-level="D" data-path="remote-server.html"><a href="remote-server.html"><i class="fa fa-check"></i><b>D</b> Using Remote Server</a><ul>
<li class="chapter" data-level="D.1" data-path="remote-server.html"><a href="remote-server.html#server-setup"><i class="fa fa-check"></i><b>D.1</b> Server Setup</a></li>
<li class="chapter" data-level="D.2" data-path="remote-server.html"><a href="remote-server.html#connecting-to-the-remote-server"><i class="fa fa-check"></i><b>D.2</b> Connecting to the Remote Server</a></li>
<li class="chapter" data-level="D.3" data-path="remote-server.html"><a href="remote-server.html#copying-files"><i class="fa fa-check"></i><b>D.3</b> Copying Files</a><ul>
<li class="chapter" data-level="D.3.1" data-path="remote-server.html"><a href="remote-server.html#scp"><i class="fa fa-check"></i><b>D.3.1</b> scp</a></li>
<li class="chapter" data-level="D.3.2" data-path="remote-server.html"><a href="remote-server.html#rsync"><i class="fa fa-check"></i><b>D.3.2</b> rsync</a></li>
<li class="chapter" data-level="D.3.3" data-path="remote-server.html"><a href="remote-server.html#graphical-frontends"><i class="fa fa-check"></i><b>D.3.3</b> Graphical Frontends</a></li>
<li class="chapter" data-level="D.3.4" data-path="remote-server.html"><a href="remote-server.html#remote-editing"><i class="fa fa-check"></i><b>D.3.4</b> Remote Editing</a></li>
</ul></li>
<li class="chapter" data-level="D.4" data-path="remote-server.html"><a href="remote-server.html#r-and-rscript"><i class="fa fa-check"></i><b>D.4</b> R and Rscript</a><ul>
<li class="chapter" data-level="D.4.1" data-path="remote-server.html"><a href="remote-server.html#graphics-output-with-no-gui"><i class="fa fa-check"></i><b>D.4.1</b> Graphics Output with No GUI</a></li>
</ul></li>
<li class="chapter" data-level="D.5" data-path="remote-server.html"><a href="remote-server.html#life-on-server"><i class="fa fa-check"></i><b>D.5</b> Life on Server</a><ul>
<li class="chapter" data-level="D.5.1" data-path="remote-server.html"><a href="remote-server.html#be-social"><i class="fa fa-check"></i><b>D.5.1</b> Be Social!</a></li>
<li class="chapter" data-level="D.5.2" data-path="remote-server.html"><a href="remote-server.html#useful-things-to-do"><i class="fa fa-check"></i><b>D.5.2</b> Useful Things to Do</a></li>
<li class="chapter" data-level="D.5.3" data-path="remote-server.html"><a href="remote-server.html#permissions-and-ownership"><i class="fa fa-check"></i><b>D.5.3</b> Permissions and ownership</a></li>
<li class="chapter" data-level="D.5.4" data-path="remote-server.html"><a href="remote-server.html#more-than-one-connection"><i class="fa fa-check"></i><b>D.5.4</b> More than One Connection</a></li>
</ul></li>
<li class="chapter" data-level="D.6" data-path="remote-server.html"><a href="remote-server.html#advanced-usage"><i class="fa fa-check"></i><b>D.6</b> Advanced Usage</a><ul>
<li class="chapter" data-level="D.6.1" data-path="remote-server.html"><a href="remote-server.html#ssh-keys-.sshconfig"><i class="fa fa-check"></i><b>D.6.1</b> ssh keys, .ssh/config</a></li>
<li class="chapter" data-level="D.6.2" data-path="remote-server.html"><a href="remote-server.html#more-about-command-line-pipes-and-shell-patterns"><i class="fa fa-check"></i><b>D.6.2</b> More about command line: pipes and shell patterns</a></li>
<li class="chapter" data-level="D.6.3" data-path="remote-server.html"><a href="remote-server.html#running-rscript-in-ssh-session"><i class="fa fa-check"></i><b>D.6.3</b> Running RScript in ssh Session</a></li>
</ul></li>
</ul></li>
<li class="divider"></li>
<li><a href="https://github.com/rstudio/bookdown" target="blank">Published with bookdown</a></li>

</ul>

      </nav>
    </div>

    <div class="book-body">
      <div class="body-inner">
        <div class="book-header" role="navigation">
          <h1>
            <i class="fa fa-circle-o-notch fa-spin"></i><a href="./">Technical Foundations of Informatics</a>
          </h1>
        </div>

        <div class="page-wrapper" tabindex="-1" role="main">
          <div class="page-inner">

            <section class="normal" id="section-">
<div id="data-frames" class="section level1">
<h1><span class="header-section-number">Chapter 9</span> Data Frames</h1>
<p>This chapter introduces <strong>data frame</strong> objects, which are the primary data storage type used in R. In many ways, data frames are similar to a two-dimensional row/column layout that you should be familiar with from spreadsheet programs like Microsoft Excel. Rather than interact with this data structure through a UI, we’ll learn how to programmatically and reproducibly perform operations on this data type. This chapter covers various ways of creating, describing, and accessing data frames, as well as how they are related to other data types in R.</p>
<div id="what-is-a-data-frame" class="section level2">
<h2><span class="header-section-number">9.1</span> What is a Data Frame?</h2>
<p>At a practical level, <strong>Data Frames</strong> act like <em>tables</em>, where data is organized into rows and columns. For example, consider the following table of names, weights, and heights:</p>
<div class="figure">
<img src="img/dataframes/table-example.png" title="table of weights and heights" alt="A table of data (people’s weights and heights)." />
<p class="caption">A table of data (people’s weights and heights).</p>
</div>
<p>In this table, each <em>row</em> represents a <strong>record</strong> or <strong>observation</strong>: an instance of a single thing being measured (e.g., a person). Each <em>column</em> represents a <strong>feature</strong>: a particular property or aspect of the thing being measured (e.g., the person’s height or weight). This structure is used to organize lots of different <em>related</em> data points for easier analysis.</p>
<p>In R, you can use <strong>data frames</strong> to represent these kinds of tables. Data frames are really just <strong>lists</strong> (see <a href="lists.html#lists">Lists</a>) in which each element is a <strong>vector of the same length</strong>. Each vector represents a <strong>column, <em>not</em> a row</strong>. The elements at corresponding indices in the vectors are considered part of the same record (row).</p>
<ul>
<li>This makes sense because each row may have a different type of data—e.g., a person’s <code>name</code> (string) and <code>height</code> (number)—and vector elements must all be of the same type.</li>
</ul>
<p>For example, you can think of the above table as a <em>list</em> of three <em>vectors</em>: <code>name</code>, <code>height</code> and <code>weight</code>. The name, height, and weight of the first person measured are represented by the first elements of the <code>name</code>, <code>height</code> and <code>weight</code> vectors respectively.</p>
<p>You can work with data frames as if they were lists, but data frames include additional properties as well that make them particularly well suited for handling tables of data.</p>
<div id="creating-data-frames" class="section level3">
<h3><span class="header-section-number">9.1.1</span> Creating Data Frames</h3>
<p>Typically you will <em>load</em> data sets from some external source (see <a href="data-frames.html#csv-files">below</a>), rather than writing out the data by hand. However, it is important to understand that you can construct a data frame by combining multiple vectors. To accomplish this, you can use the <code>data.frame()</code> function, which accepts <strong>vectors</strong> as <em>arguments</em>, and creates a table with a column for each vector. For example:</p>
<div class="sourceCode" id="cb100"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb100-1" data-line-number="1"><span class="co"># vector of names</span></a>
<a class="sourceLine" id="cb100-2" data-line-number="2">name &lt;-<span class="st"> </span><span class="kw">c</span>(<span class="st">&quot;Ada&quot;</span>, <span class="st">&quot;Bob&quot;</span>, <span class="st">&quot;Chris&quot;</span>, <span class="st">&quot;Diya&quot;</span>, <span class="st">&quot;Emma&quot;</span>)</a>
<a class="sourceLine" id="cb100-3" data-line-number="3"></a>
<a class="sourceLine" id="cb100-4" data-line-number="4"><span class="co"># Vector of heights</span></a>
<a class="sourceLine" id="cb100-5" data-line-number="5">height &lt;-<span class="st"> </span><span class="dv">58</span><span class="op">:</span><span class="dv">62</span></a>
<a class="sourceLine" id="cb100-6" data-line-number="6"></a>
<a class="sourceLine" id="cb100-7" data-line-number="7"><span class="co"># Vector of weights</span></a>
<a class="sourceLine" id="cb100-8" data-line-number="8">weight &lt;-<span class="st"> </span><span class="kw">c</span>(<span class="dv">115</span>, <span class="dv">117</span>, <span class="dv">120</span>, <span class="dv">123</span>, <span class="dv">126</span>)</a>
<a class="sourceLine" id="cb100-9" data-line-number="9"></a>
<a class="sourceLine" id="cb100-10" data-line-number="10"><span class="co"># Combine the vectors into a data.frame</span></a>
<a class="sourceLine" id="cb100-11" data-line-number="11"><span class="co"># Note the names of the variables become the names of the columns!</span></a>
<a class="sourceLine" id="cb100-12" data-line-number="12">my_data &lt;-<span class="st"> </span><span class="kw">data.frame</span>(name, height, weight, <span class="dt">stringsAsFactors =</span> <span class="ot">FALSE</span>)</a></code></pre></div>
<ul>
<li>(The last argument to the <code>data.frame()</code> function is included because one of the vectors contains strings; it tells R to treat that vector as a <em>vector</em> not as a <strong>factor</strong>. This is usually what you’ll want to do. See below for details about <a href="data-frames.html#factors">factors</a>).</li>
</ul>
<p>Because data frame elements are lists, you can access the values from <code>my_data</code> using the same <strong>dollar notation</strong> and <strong>double-bracket notation</strong> as lists:</p>
<div class="sourceCode" id="cb101"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb101-1" data-line-number="1"><span class="co"># Using the same weights/heights as above:</span></a>
<a class="sourceLine" id="cb101-2" data-line-number="2">my_data &lt;-<span class="st"> </span><span class="kw">data.frame</span>(height, weight)</a>
<a class="sourceLine" id="cb101-3" data-line-number="3"></a>
<a class="sourceLine" id="cb101-4" data-line-number="4"><span class="co"># Retrieve weights (the `weight` element of the list: a vector!)</span></a>
<a class="sourceLine" id="cb101-5" data-line-number="5">my_weights &lt;-<span class="st"> </span>my_data<span class="op">$</span>weight</a>
<a class="sourceLine" id="cb101-6" data-line-number="6"></a>
<a class="sourceLine" id="cb101-7" data-line-number="7"><span class="co"># Retrieve heights (the whole column: a vector!)</span></a>
<a class="sourceLine" id="cb101-8" data-line-number="8">my_heights &lt;-<span class="st"> </span>my_data[[<span class="st">&quot;height&quot;</span>]]</a></code></pre></div>
</div>
<div id="describing-structure-of-data-frames" class="section level3">
<h3><span class="header-section-number">9.1.2</span> Describing Structure of Data Frames</h3>
<p>While you can interact with data frames as lists, they also offer a number of additional capabilities and functions. For example, here are a few ways you can <em>inspect</em> the structure of a data frame:</p>
<table>
<colgroup>
<col width="5%" />
<col width="94%" />
</colgroup>
<thead>
<tr class="header">
<th align="left">Function</th>
<th align="left">Description</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left"><code>nrow(my_data_frame)</code></td>
<td align="left">Number of rows in the data frame</td>
</tr>
<tr class="even">
<td align="left"><code>ncol(my_data_frame)</code></td>
<td align="left">Number of columns in the data frame</td>
</tr>
<tr class="odd">
<td align="left"><code>dim(my_data_frame)</code></td>
<td align="left">Dimensions (rows, columns) in the data frame</td>
</tr>
<tr class="even">
<td align="left"><code>colnames(my_data_frame)</code></td>
<td align="left">Names of the columns of the data frame</td>
</tr>
<tr class="odd">
<td align="left"><code>rownames(my_data_frame)</code></td>
<td align="left">Names of the row of the data frame</td>
</tr>
<tr class="even">
<td align="left"><code>head(my_data_frame)</code></td>
<td align="left">Extracts the first few rows of the data frame (as a new data frame)</td>
</tr>
<tr class="odd">
<td align="left"><code>tail(my_data_frame)</code></td>
<td align="left">Extracts the last few rows of the data frame (as a new data frame)</td>
</tr>
<tr class="even">
<td align="left"><code>View(my_data_frame)</code></td>
<td align="left">Opens the data frame in as spreadsheet-like viewer (only in RStudio)</td>
</tr>
</tbody>
</table>
<p>Note that many of these description functions can also be used to <em>modify</em> the structure of a data frame. For example, you can use the <code>colnames</code> functions to assign a new set of column names to a data frame:</p>
<div class="sourceCode" id="cb102"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb102-1" data-line-number="1"><span class="co"># Using the same weights/heights as above:</span></a>
<a class="sourceLine" id="cb102-2" data-line-number="2">my_data &lt;-<span class="st"> </span><span class="kw">data.frame</span>(name, height, weight)</a>
<a class="sourceLine" id="cb102-3" data-line-number="3"></a>
<a class="sourceLine" id="cb102-4" data-line-number="4"><span class="co"># A vector of new column names</span></a>
<a class="sourceLine" id="cb102-5" data-line-number="5">new_col_names &lt;-<span class="st"> </span><span class="kw">c</span>(<span class="st">&#39;first_name&#39;</span>,<span class="st">&#39;how_tall&#39;</span>,<span class="st">&#39;how_heavy&#39;</span>)</a>
<a class="sourceLine" id="cb102-6" data-line-number="6"></a>
<a class="sourceLine" id="cb102-7" data-line-number="7"><span class="co"># Assign that vector to be the vector of column names</span></a>
<a class="sourceLine" id="cb102-8" data-line-number="8"><span class="kw">colnames</span>(my_data) &lt;-<span class="st"> </span>new_col_names</a></code></pre></div>
</div>
<div id="accessing-data-in-data-frames" class="section level3">
<h3><span class="header-section-number">9.1.3</span> Accessing Data in Data Frames</h3>
<p>As stated above, since data frames <em>are</em> lists, it’s possible to use <strong>dollar notation</strong> (<code>my_data_frame$column_name</code>) or <strong>double-bracket notation</strong> (<code>my_data_frame[['column_name']]</code>) to access entire columns. However, R also uses a variation of <strong>single-bracket notation</strong> which allows you to access individual data elements (cells) in the table. In this syntax, you put <em>two</em> values separated by a comma (<strong><code>,</code></strong>) inside the brackets—the first for which row and the second for which column you wish you extract:</p>
<table>
<colgroup>
<col width="30%" />
<col width="28%" />
<col width="40%" />
</colgroup>
<thead>
<tr class="header">
<th align="left">Syntax</th>
<th align="left">Description</th>
<th align="left">Example</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td align="left"><code>my_df[row_num, col_num]</code></td>
<td align="left">Element by row and column indices</td>
<td align="left"><code>my_frame[2,3]</code> (element in the second row, third column)</td>
</tr>
<tr class="even">
<td align="left"><code>my_df[row_name, col_name]</code></td>
<td align="left">Element by row and column names</td>
<td align="left"><code>my_frame['Ada','height']</code> (element in row <em>named</em> <code>Ada</code> and column <em>named</em> <code>height</code>; the <code>height</code> of <code>Ada</code>)</td>
</tr>
<tr class="odd">
<td align="left"><code>my_df[row, col]</code></td>
<td align="left">Element by row and col; can mix indices and names</td>
<td align="left"><code>my_frame[2,'height']</code> (second element in the <code>height</code> column)</td>
</tr>
<tr class="even">
<td align="left"><code>my_df[row, ]</code></td>
<td align="left">All elements (columns) in row index or name</td>
<td align="left"><code>my_frame[2,]</code> (all columns in the second row)</td>
</tr>
<tr class="odd">
<td align="left"><code>my_df[, col]</code></td>
<td align="left">All elements (rows) in a col index or name</td>
<td align="left"><code>my_frame[,'height']</code> (all rows in the <code>height</code> column; equivalent to list notations)</td>
</tr>
</tbody>
</table>
<p>Take special note of the 4th option’s syntax (for retrieving rows): you still include the comma (<code>,</code>), but because you leave <em>which column</em> blank, you get all of the columns!</p>
<div class="sourceCode" id="cb103"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb103-1" data-line-number="1"><span class="co"># Extract the second row</span></a>
<a class="sourceLine" id="cb103-2" data-line-number="2">my_data[<span class="dv">2</span>, ] <span class="co"># comma</span></a>
<a class="sourceLine" id="cb103-3" data-line-number="3"></a>
<a class="sourceLine" id="cb103-4" data-line-number="4"><span class="co"># Extract the second column AS A VECTOR</span></a>
<a class="sourceLine" id="cb103-5" data-line-number="5">my_data[, <span class="dv">2</span>] <span class="co"># comma</span></a>
<a class="sourceLine" id="cb103-6" data-line-number="6"></a>
<a class="sourceLine" id="cb103-7" data-line-number="7"><span class="co"># Extract the second column AS A DATA FRAME (filtering)</span></a>
<a class="sourceLine" id="cb103-8" data-line-number="8">my_data[<span class="dv">2</span>] <span class="co"># no comma</span></a></code></pre></div>
<p>(Extracting from more than one column will produce a <em>sub-data frame</em>; extracting from just one column will produce a vector).</p>
<p>And of course, because <em>everything is a vector</em>, you’re actually specifying vectors of indices to extract. This allows you to get multiple rows or columns:</p>
<div class="sourceCode" id="cb104"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb104-1" data-line-number="1"><span class="co"># Get the second through fourth rows</span></a>
<a class="sourceLine" id="cb104-2" data-line-number="2">my_data[<span class="dv">2</span><span class="op">:</span><span class="dv">4</span>, ]</a>
<a class="sourceLine" id="cb104-3" data-line-number="3"></a>
<a class="sourceLine" id="cb104-4" data-line-number="4"><span class="co"># Get the `height` and `weight` columns</span></a>
<a class="sourceLine" id="cb104-5" data-line-number="5">my_data[, <span class="kw">c</span>(<span class="st">&quot;height&quot;</span>, <span class="st">&quot;weight&quot;</span>)]</a>
<a class="sourceLine" id="cb104-6" data-line-number="6"></a>
<a class="sourceLine" id="cb104-7" data-line-number="7"><span class="co"># Perform filtering</span></a>
<a class="sourceLine" id="cb104-8" data-line-number="8">my_data[my_data<span class="op">$</span>height <span class="op">&gt;</span><span class="st"> </span><span class="dv">60</span>, ] <span class="co"># rows for which `height` is greater than 60</span></a></code></pre></div>
</div>
</div>
<div id="csv-files" class="section level2">
<h2><span class="header-section-number">9.2</span> Working with CSV Data</h2>
<p>So far you’ve been constructing your own data frames by “hard-coding” the data values. But it’s much more common to load that data from somewhere else, such as a separate file on your computer or by downloading it off the internet. While R is able to ingest data from a variety of sources, this chapter will focus on reading tabular data in <strong>comma separated value</strong> (CSV) format, usually stored in a <code>.csv</code> file. In this format, each line of the file represents a record (<em>row</em>) of data, while each feature (<em>column</em>) of that record is separated by a comma:</p>
<pre><code>Ada, 58, 115
Bob, 59, 117
Chris, 60, 120
Diya, 61, 123
Emma, 62, 126</code></pre>
<p>Most spreadsheet programs like Microsoft Excel, Numbers, or Google Sheets are simply interfaces for formatting and interacting with data that is saved in this format. These programs easily import and export <code>.csv</code> files; however <code>.csv</code> files are unable to save the formatting done in those programs—the files only store the data!</p>
<p>You can load the data from a <code>.csv</code> file into R by using the <code>read.csv()</code> function:</p>
<div class="sourceCode" id="cb106"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb106-1" data-line-number="1"><span class="co"># Read data from the file `my_file.csv` into a data frame `my_data`</span></a>
<a class="sourceLine" id="cb106-2" data-line-number="2">my_data &lt;-<span class="st"> </span><span class="kw">read.csv</span>(<span class="st">&#39;my_file.csv&#39;</span>, <span class="dt">stringsAsFactors=</span><span class="ot">FALSE</span>)</a></code></pre></div>
<p>Again, use the <code>stringsAsFactors</code> argument to make sure string data is stored as a <em>vector</em> rather than as a <em>factor</em> (see <a href="data-frames.html#factors">below</a>). This function will return a data frame, just like those described above!</p>
<p class="alert alert-warning">
<strong>Important Note</strong>: If for whatever reason an element is missing from a data frame (which is very common with real world data!), R will fill that cell with the logical value <code>NA</code> (distinct from the string <code>&quot;NA&quot;</code>), meaning “<strong>N</strong>ot <strong>A</strong>vailable”. There are multiple ways to handle this in an analysis; see <a href="http://www.statmethods.net/input/missingdata.html">this link</a> among others for details.
</p>
<div id="working-directory" class="section level3">
<h3><span class="header-section-number">9.2.1</span> Working Directory</h3>
<p>The biggest complication when loading <code>.csv</code> files is that the <code>read.csv()</code> function takes as an argument a <strong>path</strong> to the file. Because you want this script to work on any computer (to support collaboration, as well as things like assignment grading), you need to be sure to use a <strong>relative path</strong> to the file. The question is: <em>relative to what</em>?</p>
<p>Like the command-line, the R interpreter (running inside R Studio) has a <strong>current working directory</strong> from which all file paths are relative. The trick is that <strong><em>the working directory is not the directory of the current script file!</em></strong></p>
<ul>
<li>This makes sense if you think about it: you can run R commands through the console without having a script, and you can have open multiple script files from separate folders that are all interacting with the same execution environment.</li>
</ul>
<p>Just as you can view the current working directory when on the command line (using <code>pwd</code>), you can use an R function to view the current working directory when in R:</p>
<div class="sourceCode" id="cb107"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb107-1" data-line-number="1"><span class="co"># get the absolute path to the current working directory</span></a>
<a class="sourceLine" id="cb107-2" data-line-number="2"><span class="kw">getwd</span>()</a></code></pre></div>
<p>You often will want to change the working directory to be your “project” directory (wherever your scripts and data files happen to be). It is possible to change the current working directory using the <code>setwd()</code> function. However, this function would also take an absolute path, so doesn’t fix the problem. You would not want to include this absolute path in your script (though you could use it from the console).</p>
<p>One solution is to use the tilde (<code>~</code>) shortcut to specify your directory:</p>
<div class="sourceCode" id="cb108"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb108-1" data-line-number="1"><span class="co"># Set working directory on Desktop</span></a>
<a class="sourceLine" id="cb108-2" data-line-number="2"><span class="kw">setwd</span>(<span class="st">&quot;~/Desktop/project-name&quot;</span>)</a></code></pre></div>
<p>This enables you to work across machines, as long as the project is stored in the same location on each machine.</p>
<p>Another solution is to use R Studio itself to change the working directory. This is reasonable because the working directory is a property of the <em>current running environment</em>, which is what R Studio makes accessible! The easiest way to do this is to use the <strong><code>Session &gt; Set Working Directory</code></strong> menu options: you can either set the working directory <code>To Source File Location</code> (the folder containing whichever <code>.R</code> script you are currently editing; this is usually what you want), or you can browse for a particular directory with <code>Choose Directory</code>.</p>
<div class="figure">
<img src="img/dataframes/session-setwd-rstudio.png" alt="Use Session &gt; Set Working Directory to change the working directory through R Studio" />
<p class="caption">Use <code>Session &gt; Set Working Directory</code> to change the working directory through R Studio</p>
</div>
<p>You should do this whenever you hit a “path” problem when loading external files. If you want to do this repeatedly by calling <code>setwd()</code> from your script to an absolute path, you may want to keep it commented out (<code># setwd(...)</code>) so it doesn’t cause problems for others who try to run your script.</p>
</div>
</div>
<div id="factors" class="section level2">
<h2><span class="header-section-number">9.3</span> Factor Variables</h2>
<p><strong>Factors</strong> are a way of <em>optimizing</em> variables that consist of a finite set of categories (i.e., they are <strong>categorical (nominal) variables</strong>).</p>
<p>For example, imagine that you had a vector of shirt sizes which could only take on the values <code>small</code>, <code>medium</code>, or <code>large</code>. If you were working with a large dataset (thousands of shirts!), it would end up taking up a lot of memory to store the character strings (5+ letters per word at 1 or more bytes per letter) for each one of those variables.</p>
<p>A <strong>factor</strong> on the other hand would instead store a <em>number</em> (called a <strong>level</strong>) for each of these character strings: for example, <code>1</code> for <code>small</code>, <code>2</code> for <code>medium</code>, or <code>3</code> for <code>large</code> (though the order or specific numbers will vary). R will remember the relationship between the integers and their <strong>labels</strong> (the strings). Since each number only takes 4 bytes (rather than 1 per letter), factors allow R to keep much more information in memory.</p>
<div class="sourceCode" id="cb109"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb109-1" data-line-number="1"><span class="co"># Start with a character vector of shirt sizes</span></a>
<a class="sourceLine" id="cb109-2" data-line-number="2">shirt_sizes &lt;-<span class="st"> </span><span class="kw">c</span>(<span class="st">&quot;small&quot;</span>, <span class="st">&quot;medium&quot;</span>, <span class="st">&quot;small&quot;</span>, <span class="st">&quot;large&quot;</span>, <span class="st">&quot;medium&quot;</span>, <span class="st">&quot;large&quot;</span>)</a>
<a class="sourceLine" id="cb109-3" data-line-number="3"></a>
<a class="sourceLine" id="cb109-4" data-line-number="4"><span class="co"># Convert to a vector of factor data</span></a>
<a class="sourceLine" id="cb109-5" data-line-number="5">shirt_sizes_factor &lt;-<span class="st"> </span><span class="kw">as.factor</span>(shirt_sizes)</a>
<a class="sourceLine" id="cb109-6" data-line-number="6"></a>
<a class="sourceLine" id="cb109-7" data-line-number="7"><span class="co"># View the factor and its levels</span></a>
<a class="sourceLine" id="cb109-8" data-line-number="8"><span class="kw">print</span>(shirt_sizes_factor)</a>
<a class="sourceLine" id="cb109-9" data-line-number="9"></a>
<a class="sourceLine" id="cb109-10" data-line-number="10"><span class="co"># The length of the factor is still the length of the vector, not the number of levels</span></a>
<a class="sourceLine" id="cb109-11" data-line-number="11"><span class="kw">length</span>(shirt_sizes_factor) <span class="co"># 6</span></a></code></pre></div>
<p>When you print out the <code>shirt_sizes_factor</code> variable, R still (intelligently) prints out the <strong>labels</strong> that you are presumably interested in. It also indicates the <strong>levels</strong>, which are the <em>only</em> possible values that elements can take on.</p>
<p>It is worth re-stating: <strong>factors are not vectors</strong>. This means that most all the operations and functions you want to use on vectors <em>will not work</em>:</p>
<div class="sourceCode" id="cb110"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb110-1" data-line-number="1"><span class="co"># Create a factor of numbers (factors need not be strings)</span></a>
<a class="sourceLine" id="cb110-2" data-line-number="2">num_factors &lt;-<span class="st"> </span><span class="kw">as.factor</span>(<span class="kw">c</span>(<span class="dv">10</span>,<span class="dv">10</span>,<span class="dv">20</span>,<span class="dv">20</span>,<span class="dv">30</span>,<span class="dv">30</span>,<span class="dv">40</span>,<span class="dv">40</span>))</a>
<a class="sourceLine" id="cb110-3" data-line-number="3"></a>
<a class="sourceLine" id="cb110-4" data-line-number="4"><span class="co"># Print the factor to see its levels</span></a>
<a class="sourceLine" id="cb110-5" data-line-number="5"><span class="kw">print</span>(num_factors)</a>
<a class="sourceLine" id="cb110-6" data-line-number="6"></a>
<a class="sourceLine" id="cb110-7" data-line-number="7"><span class="co"># Multiply the numbers by 2</span></a>
<a class="sourceLine" id="cb110-8" data-line-number="8">num_factors <span class="op">*</span><span class="st"> </span><span class="dv">2</span>  <span class="co"># Error: * not meaningful</span></a>
<a class="sourceLine" id="cb110-9" data-line-number="9">                 <span class="co"># returns vector of NA instead</span></a>
<a class="sourceLine" id="cb110-10" data-line-number="10"></a>
<a class="sourceLine" id="cb110-11" data-line-number="11"><span class="co"># Changing entry to a level is fine</span></a>
<a class="sourceLine" id="cb110-12" data-line-number="12">num_factors[<span class="dv">1</span>] &lt;-<span class="st"> </span><span class="dv">40</span></a>
<a class="sourceLine" id="cb110-13" data-line-number="13"></a>
<a class="sourceLine" id="cb110-14" data-line-number="14"><span class="co"># Change entry to a value that ISN&#39;T a level fails</span></a>
<a class="sourceLine" id="cb110-15" data-line-number="15">num_factors[<span class="dv">1</span>] &lt;-<span class="st"> </span><span class="dv">50</span>  <span class="co"># Error: invalid factor level</span></a>
<a class="sourceLine" id="cb110-16" data-line-number="16">                      <span class="co"># num_factors[1] is now NA</span></a></code></pre></div>
<p>If you create a data frame with a string vector as a column (as what happens with <code>read.csv()</code>), it will automatically be treated as a factor <em>unless you explicitly tell it not to</em>:</p>
<div class="sourceCode" id="cb111"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb111-1" data-line-number="1"><span class="co"># Vector of shirt sizes</span></a>
<a class="sourceLine" id="cb111-2" data-line-number="2">shirt_size &lt;-<span class="st"> </span><span class="kw">c</span>(<span class="st">&quot;small&quot;</span>, <span class="st">&quot;medium&quot;</span>, <span class="st">&quot;small&quot;</span>, <span class="st">&quot;large&quot;</span>, <span class="st">&quot;medium&quot;</span>, <span class="st">&quot;large&quot;</span>)</a>
<a class="sourceLine" id="cb111-3" data-line-number="3"></a>
<a class="sourceLine" id="cb111-4" data-line-number="4"><span class="co"># Vector of costs (in dollars)</span></a>
<a class="sourceLine" id="cb111-5" data-line-number="5">cost &lt;-<span class="st"> </span><span class="kw">c</span>(<span class="fl">15.5</span>, <span class="dv">17</span>, <span class="dv">17</span>, <span class="dv">14</span>, <span class="dv">12</span>, <span class="dv">23</span>)</a>
<a class="sourceLine" id="cb111-6" data-line-number="6"></a>
<a class="sourceLine" id="cb111-7" data-line-number="7"><span class="co"># Data frame of inventory (with factors, since didn&#39;t say otherwise)</span></a>
<a class="sourceLine" id="cb111-8" data-line-number="8">shirts_factor &lt;-<span class="st"> </span><span class="kw">data.frame</span>(shirt_size, cost)</a>
<a class="sourceLine" id="cb111-9" data-line-number="9"></a>
<a class="sourceLine" id="cb111-10" data-line-number="10"><span class="co"># The shirt_size column is a factor</span></a>
<a class="sourceLine" id="cb111-11" data-line-number="11"><span class="kw">is.factor</span>(shirts_factor<span class="op">$</span>shirt_size) <span class="co"># TRUE</span></a>
<a class="sourceLine" id="cb111-12" data-line-number="12"></a>
<a class="sourceLine" id="cb111-13" data-line-number="13"><span class="co"># Can treat this as a vector; but better to fix how the data is loaded</span></a>
<a class="sourceLine" id="cb111-14" data-line-number="14"><span class="kw">as.vector</span>(shirts_factor<span class="op">$</span>shirt_size) <span class="co"># a vector</span></a>
<a class="sourceLine" id="cb111-15" data-line-number="15"></a>
<a class="sourceLine" id="cb111-16" data-line-number="16"><span class="co"># Data frame of orders (without factoring)</span></a>
<a class="sourceLine" id="cb111-17" data-line-number="17">shirts &lt;-<span class="st"> </span><span class="kw">data.frame</span>(shirt_size, cost, <span class="dt">stringsAsFactors =</span> <span class="ot">FALSE</span>)</a>
<a class="sourceLine" id="cb111-18" data-line-number="18"></a>
<a class="sourceLine" id="cb111-19" data-line-number="19"><span class="co"># The shirt_size column is NOT a factor</span></a>
<a class="sourceLine" id="cb111-20" data-line-number="20"><span class="kw">is.factor</span>(shirts<span class="op">$</span>shirt_size) <span class="co"># FALSE</span></a></code></pre></div>
<p>This is not to say that factors can’t be useful (beyond just saving memory)! They offer easy ways to group and process data using specialized functions:</p>
<div class="sourceCode" id="cb112"><pre class="sourceCode r"><code class="sourceCode r"><a class="sourceLine" id="cb112-1" data-line-number="1">shirt_size &lt;-<span class="st"> </span><span class="kw">c</span>(<span class="st">&quot;small&quot;</span>, <span class="st">&quot;medium&quot;</span>, <span class="st">&quot;small&quot;</span>, <span class="st">&quot;large&quot;</span>, <span class="st">&quot;medium&quot;</span>, <span class="st">&quot;large&quot;</span>)</a>
<a class="sourceLine" id="cb112-2" data-line-number="2">cost &lt;-<span class="st"> </span><span class="kw">c</span>(<span class="fl">15.5</span>, <span class="dv">17</span>, <span class="dv">17</span>, <span class="dv">14</span>, <span class="dv">12</span>, <span class="dv">23</span>)</a>
<a class="sourceLine" id="cb112-3" data-line-number="3"></a>
<a class="sourceLine" id="cb112-4" data-line-number="4"><span class="co"># Data frame of inventory (with factors)</span></a>
<a class="sourceLine" id="cb112-5" data-line-number="5">shirts_factor &lt;-<span class="st"> </span><span class="kw">data.frame</span>(shirt_size, cost)</a>
<a class="sourceLine" id="cb112-6" data-line-number="6"></a>
<a class="sourceLine" id="cb112-7" data-line-number="7"><span class="co"># Produce a list of data frames, one for each factor level</span></a>
<a class="sourceLine" id="cb112-8" data-line-number="8"><span class="co"># first argument is the data frame to split, second is the factor to split by</span></a>
<a class="sourceLine" id="cb112-9" data-line-number="9">shirt_size_frames &lt;-<span class="st"> </span><span class="kw">split</span>(shirts_factor, shirts_factor<span class="op">$</span>shirt_size)</a>
<a class="sourceLine" id="cb112-10" data-line-number="10"></a>
<a class="sourceLine" id="cb112-11" data-line-number="11"></a>
<a class="sourceLine" id="cb112-12" data-line-number="12"><span class="co"># Apply a function (mean) to each factor level</span></a>
<a class="sourceLine" id="cb112-13" data-line-number="13"><span class="co">#   first argument is the vector to apply the function to,</span></a>
<a class="sourceLine" id="cb112-14" data-line-number="14"><span class="co">#   second argument is the factor to split by</span></a>
<a class="sourceLine" id="cb112-15" data-line-number="15"><span class="co">#   third argument is the name of the function</span></a>
<a class="sourceLine" id="cb112-16" data-line-number="16"><span class="kw">tapply</span>(shirts_factor<span class="op">$</span>cost, shirts_factor<span class="op">$</span>shirt_size, mean)</a></code></pre></div>
<p>However, in general this course is more interested in working with data as vectors, thus you should always use <code>stringsAsFactors=FALSE</code> when creating data frames or loading <code>.csv</code> files that include strings.</p>
</div>
<div id="resources-8" class="section level2 unnumbered">
<h2>Resources</h2>
<ul>
<li><a href="http://www.r-tutor.com/r-introduction/data-frame">R Tutorial: Data Frames</a></li>
<li><a href="http://www.r-tutor.com/r-introduction/data-frame/data-frame-row-slice">R Tutorial: Data Frame Indexing</a></li>
<li><a href="http://www.statmethods.net/input/missingdata.html">Quick-R: Missing Values</a></li>
<li><a href="http://www.ats.ucla.edu/stat/r/modules/factor_variables.htm">Factor Variables (UCLA)</a></li>
</ul>

</div>
</div>
            </section>

          </div>
        </div>
      </div>
<a href="lists.html" class="navigation navigation-prev " aria-label="Previous page"><i class="fa fa-angle-left"></i></a>
<a href="dplyr.html" class="navigation navigation-next " aria-label="Next page"><i class="fa fa-angle-right"></i></a>
    </div>
  </div>
<script src="libs/gitbook-2.6.7/js/app.min.js"></script>
<script src="libs/gitbook-2.6.7/js/lunr.js"></script>
<script src="libs/gitbook-2.6.7/js/plugin-search.js"></script>
<script src="libs/gitbook-2.6.7/js/plugin-sharing.js"></script>
<script src="libs/gitbook-2.6.7/js/plugin-fontsettings.js"></script>
<script src="libs/gitbook-2.6.7/js/plugin-bookdown.js"></script>
<script src="libs/gitbook-2.6.7/js/jquery.highlight.js"></script>
<script>
gitbook.require(["gitbook"], function(gitbook) {
gitbook.start({
"sharing": {
"github": true,
"facebook": false,
"twitter": false,
"google": false,
"linkedin": false,
"weibo": false,
"instapaper": false,
"vk": false,
"all": ["github", "facebook", "twitter", "google"]
},
"fontsettings": {
"theme": "white",
"family": "sans",
"size": 2
},
"edit": {
"link": "https://github.com/info201/book/edit/master/dataframes.Rmd",
"text": "Edit"
},
"history": {
"link": null,
"text": null
},
"download": null,
"toc": {
"collapse": "section",
"scroll_highlight": true
}
});
});
</script>

</body>

</html>