Getting the count of unique values in a column in bash - bash

Question

I have tab delimited files with several columns. I want to count the frequency of occurrence of the different values in a column for all the files in a folder and sort them in decreasing order of count (highest count first). How would I accomplish this in a Linux command line environment?
It can use any common command line language like awk, perl, python etc.

Answer 1

To see a frequency count for column two (for example):
awk -F '\t' '{print $2}' * | sort | uniq -c | sort -nr
fileA.txt
z z a
a b c
w d e
fileB.txt
t r e
z d a
a g c
fileC.txt
z r a
v d c
a m c
Result:
3 d
2 r
1 z
1 m
1 g
1 b

Answer 2

Here is a way to do it in the shell:
FIELD=2
cut -f $FIELD * | sort| uniq -c |sort -nr
This is the sort of thing bash is great at.

Answer 3

The GNU site suggests this nice awk script, which prints both the words and their frequency.
Possible changes:
You can pipe through sort -nr (and reverse word and freq[word]) to see the result in descending order.
If you want a specific column, you can omit the for loop and simply write freq[3]++ - replace 3 with the column number.
Here goes:
# wordfreq.awk --- print list of word frequencies
{
$0 = tolower($0) # remove case distinctions
# remove punctuation
gsub(/[^[:alnum:]_[:blank:]]/, "", $0)
for (i = 1; i <= NF; i++)
freq[$i]++
}
END {
for (word in freq)
printf "%s\t%d\n", word, freq[word]
}

Answer 4

Perl
This code computes the occurrences of all columns, and prints a sorted report for each of them:
# columnvalues.pl
while (<>) {
#Fields = split /\s+/;
for $i ( 0 .. $#Fields ) {
$result[$i]{$Fields[$i]}++
};
}
for $j ( 0 .. $#result ) {
print "column $j:\n";
#values = keys %{$result[$j]};
#sorted = sort { $result[$j]{$b} <=> $result[$j]{$a} || $a cmp $b } #values;
for $k ( #sorted ) {
print " $k $result[$j]{$k}\n"
}
}
Save the text as columnvalues.pl
Run it as: perl columnvalues.pl files*
Explanation
In the top-level while loop:
* Loop over each line of the combined input files
* Split the line into the #Fields array
* For every column, increment the result array-of-hashes data structure
In the top-level for loop:
* Loop over the result array
* Print the column number
* Get the values used in that column
* Sort the values by the number of occurrences
* Secondary sort based on the value (for example b vs g vs m vs z)
* Iterate through the result hash, using the sorted list
* Print the value and number of each occurrence
Results based on the sample input files provided by #Dennis
column 0:
a 3
z 3
t 1
v 1
w 1
column 1:
d 3
r 2
b 1
g 1
m 1
z 1
column 2:
c 4
a 3
e 2
.csv input
If your input files are .csv, change /\s+/ to /,/
Obfuscation
In an ugly contest, Perl is particularly well equipped.
This one-liner does the same:
perl -lane 'for $i (0..$#F){$g[$i]{$F[$i]}++};END{for $j (0..$#g){print "$j:";for $k (sort{$g[$j]{$b}<=>$g[$j]{$a}||$a cmp $b} keys %{$g[$j]}){print " $k $g[$j]{$k}"}}}' files*

Answer 5

Ruby(1.9+)
#!/usr/bin/env ruby
Dir["*"].each do |file|
h=Hash.new(0)
open(file).each do |row|
row.chomp.split("\t").each do |w|
h[ w ] += 1
end
end
h.sort{|a,b| b[1]<=>a[1] }.each{|x,y| print "#{x}:#{y}\n" }
end

Answer 6

Here is a tricky one approaching linear time (but probably not faster!) by avoiding sort and uniq, except for the final sort. It is based on... tee and wc instead!
$ FIELD=2
$ values="$(cut -f $FIELD *)"
$ mkdir /tmp/counts
$ cd /tmp/counts
$ echo | tee -a $values
$ wc -l * | sort -nr
9 total
3 d
2 r
1 z
1 m
1 g
1 b
$

Answer 7

Pure-Bash version:
FIELD=1
declare -A results
while read -a line; do
results[${line[$FIELD]:-(empty)}]=$((results[${line[$FIELD]:-(empty)}]+1));
done < file.txt
echo ${results[#]#A}
The key logic is to fill an associative array which keys are the values found in the file and the array's value is the number of occurrence:
$FIELD is the selected column number
${line[$FIELD]} is the column value from that line in the file
${...:-(empty)} is a special case for empty values (what happens if there is less columns than expected?)
To have the output sorted in the expected OP format, a little more work is needed:
sort -rn < <(
for k in "${!results[#]}"; do
echo "${results[$k]} $k";
done
)
Warning: it works well for tab-delimited and space-delimited files, but works bad for values with spaces in it.