Counting occurrences in first column of a file

Question

We have this file:

1 2 
1 3
1 2
3 3
52 1
52 300

and 1000 more.

I want to count the number of times each value occurs in the first column.

1  3 
3  1
52 2

This means we saw 1 three times.

How can I do that, in Perl, AWK or Bash?

Answer 1

If the input is sorted, you can use uniq:

<infile cut -d' ' -f1 | uniq -c

If not, sort it first:

<infile cut -d' ' -f1 | sort -n | uniq -c

Output:

  3 1                                      
  1 3
  2 52

The output is swapped compared to your requirement, you can use awk '{ print $2, $1 }' to change that.

1 3 
3 1
52 2

There's also the awk idiom, which does not require sorted input:

awk '{h[$1]++}; END { for(k in h) print k, h[k] }'

Output:

1 3
52 2
3 1

As the output here comes from a hash it will not be ordered, pass to sort -n if that is needed:

awk '{h[$1]++} END { for(k in h) print k, h[k] }' | sort -n

If you're using GNU awk, you can do the sorting from within awk:

awk '{h[$1]++} END { n = asorti(h, d, "@ind_num_asc"); for(i=1; i<=n; i++) print d[i], h[d[i]] }'

In the last two cases the output is:

1 3
3 1
52 2