Merge pull request matplotlib#27873 from timhoffm/doc-linecollection-simple

Simplify the LineCollection example

Author: tacaswell

galleries/examples/shapes_and_collections/line_collection.py

@@ -3,79 +3,68 @@
 Plotting multiple lines with a LineCollection
 =============================================
 
-Matplotlib can efficiently draw multiple lines at once using a
-`~.LineCollection`, as showcased below.
+Matplotlib can efficiently draw multiple lines at once using a `~.LineCollection`.
 """
 
 import matplotlib.pyplot as plt
 import numpy as np
 
 from matplotlib.collections import LineCollection
 
-x = np.arange(100)
-# Here are many sets of y to plot vs. x
-ys = x[:50, np.newaxis] + x[np.newaxis, :]
+colors = ["indigo", "blue", "green", "yellow", "orange", "red"]
 
-segs = np.zeros((50, 100, 2))
-segs[:, :, 1] = ys
-segs[:, :, 0] = x
+# create a list of half-circles with varying radii
+theta = np.linspace(0, np.pi, 36)
+radii = np.linspace(4, 5, num=len(colors))
+arcs = [np.column_stack([r * np.cos(theta), r * np.sin(theta)]) for r in radii]
 
-# Mask some values to test masked array support:
-segs = np.ma.masked_where((segs > 50) & (segs < 60), segs)
+fig, ax = plt.subplots(figsize=(6.4, 3.2))
+# set axes limits manually because Collections do not take part in autoscaling
+ax.set_xlim(-6, 6)
+ax.set_ylim(0, 6)
+ax.set_aspect("equal")  # to make the arcs look circular
 
-# We need to set the plot limits, they will not autoscale
-fig, ax = plt.subplots()
-ax.set_xlim(x.min(), x.max())
-ax.set_ylim(ys.min(), ys.max())
+# create a LineCollection with the half-circles
+# its properties can be set per line by passing a sequence (here used for *colors*)
+# or they can be set for all lines by passing a scalar (here used for *linewidths*)
+line_collection = LineCollection(arcs, colors=colors, linewidths=4)
+ax.add_collection(line_collection)
 
-# *colors* is sequence of rgba tuples.
-# *linestyle* is a string or dash tuple. Legal string values are
-# solid|dashed|dashdot|dotted.  The dash tuple is (offset, onoffseq) where
-# onoffseq is an even length tuple of on and off ink in points.  If linestyle
-# is omitted, 'solid' is used.
-# See `matplotlib.collections.LineCollection` for more information.
-colors = plt.rcParams['axes.prop_cycle'].by_key()['color']
-
-line_segments = LineCollection(segs, linewidths=(0.5, 1, 1.5, 2),
-                               colors=colors, linestyle='solid')
-ax.add_collection(line_segments)
-ax.set_title('Line collection with masked arrays')
 plt.show()
 
 # %%
-# In the following example, instead of passing a list of colors
-# (``colors=colors``), we pass an array of values (``array=x``) that get
-# colormapped.
+# Instead of passing a list of colors (``colors=colors``), we can alternatively use
+# colormapping. The lines are then color-coded based on an additional array of values
+# passed to the *array* parameter. In the below example, we color the lines based on
+# their radius by passing ``array=radii``.
 
-N = 50
-x = np.arange(N)
-ys = [x + i for i in x]  # Many sets of y to plot vs. x
-segs = [np.column_stack([x, y]) for y in ys]
+num_arcs = 15
+theta = np.linspace(0, np.pi, 36)
+radii = np.linspace(4, 5.5, num=num_arcs)
+arcs = [np.column_stack([r * np.cos(theta), r * np.sin(theta)]) for r in radii]
 
-fig, ax = plt.subplots()
-ax.set_xlim(np.min(x), np.max(x))
-ax.set_ylim(np.min(ys), np.max(ys))
+fig, ax = plt.subplots(figsize=(6.4, 3))
+# set axes limits manually because Collections do not take part in autoscaling
+ax.set_xlim(-6, 6)
+ax.set_ylim(0, 6)
+ax.set_aspect("equal")  # to make the arcs look circular
 
-line_segments = LineCollection(segs, array=x,
-                               linewidths=(0.5, 1, 1.5, 2),
-                               linestyles='solid')
-ax.add_collection(line_segments)
-axcb = fig.colorbar(line_segments)
-axcb.set_label('Line Number')
-ax.set_title('Line Collection with mapped colors')
-plt.sci(line_segments)  # This allows interactive changing of the colormap.
-plt.show()
+# create a LineCollection with the half-circles and color mapping
+line_collection = LineCollection(arcs, array=radii, cmap="rainbow")
+ax.add_collection(line_collection)
 
+fig.colorbar(line_collection, label="Radius")
+ax.set_title("Line Collection with mapped colors")
+
+plt.show()
 # %%
 #
 # .. admonition:: References
 #
 #    The use of the following functions, methods, classes and modules is shown
 #    in this example:
 #
-#    - `matplotlib.collections`
 #    - `matplotlib.collections.LineCollection`
-#    - `matplotlib.cm.ScalarMappable.set_array`
+#    - `matplotlib.collections.Collection.set_array`
 #    - `matplotlib.axes.Axes.add_collection`
 #    - `matplotlib.figure.Figure.colorbar` / `matplotlib.pyplot.colorbar`
-#    - `matplotlib.pyplot.sci`