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Formatted question description: https://leetcode.ca/all/192.html

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?

Process

NAME tr – translate characters

cat words.txt

the day is sunny the the
the sunny is is

cat words.txt | tr -s ' ' '\n'

the
day
is
sunny
the
the
the
sunny
is
is

words.txt | tr -s ' ' '\n' | sort

day
is
is
is
sunny
sunny
the
the
the
the

cat words.txt | tr -s ' ' '\n' | sort | uniq -c

   1 day
   3 is
   2 sunny
   4 the

cat words.txt | tr -s ' ' '\n' | sort | uniq -c | sort -r 

   4 the
   3 is
   2 sunny
   1 day

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

the 4
is 3
sunny 2
day 1
  • here note: awk '{print $2 $1}' will generate the4, is3, adding extra spaces in between $2 $1 will not help.

Wrong answer, if missing 1st sort

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

the 3
is 2
the 1
sunny 1
sunny 1
is 1
day 1

Code

Shell

# solution-1
# tr command is mainly used for character replacement or case replacement
# -s parameter means that if consecutive characters are found, reduce them to 1
# ‘ ’ And ‘\n’ are spaces and carriage returns, which means to replace all spaces with '\n'
cat words.txt | tr -s ' ' '\n' | sort | uniq -c | sort -r | awk '{ print $2, $1 }'


# solution-2
# grep -e is strictly the flag for indicating the pattern you want to match against.
# grep -E controls whether you need to escape certain special characters.
# grep -o means: Print only the matched (non-empty) parts of a matching line, with each such part on a separate output line.
# sort -n, --numeric-sort, --sort=numeric
# sort -r, --reverse
grep -oE '[a-z]+' words.txt | sort | uniq -c | sort -nr | awk '{print $2" "$1}'

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