192-WordFrequency.sh

# 192. Word Frequency
# Write a bash script to calculate the frequency of each word in a text file words.txt.

# For simplicity sake, you may assume:
#       words.txt contains only lowercase characters and space ' ' characters.
#       Each word must consist of lowercase characters only.
#       Words are separated by one or more whitespace characters.


# Example:
# Assume that words.txt has the following content:
#   the day is sunny the the
#   the sunny is is

# Your script should output the following, sorted by descending frequency:
#   the 4
#   is 3
#   sunny 2
#   day 1

# Note:
#   Don't worry about handling ties, it is guaranteed that each word's frequency count is unique.
#   Could you write it in one-line using Unix pipes?

cat words.txt | tr -s ' ' '\n' | sort | uniq -c | sort -r | awk '{ print $2, $1 }'

# tr -s ' ' '\n' 分割词语
# sort 唯一统计前排好序 方便
# uniq -c  唯一统计
# sort -r  从大到小排序
# awk '{ print $2, $1 }' 调整输出格式

# tr -s: truncate the string with target string, but only remaining one instance (e.g. multiple whitespaces)
# sort: To make the same string successive so that uniq could count the same string fully and correctly.
# uniq -c: uniq is used to filter out the repeated lines which are successive, -c means counting
# sort -r: -r means sorting in descending order
# awk '{ print $2, $1 }': To format the output, see here.