counting the number of unique items in a list

UnixKiwi · 11-27-2008, 10:36 PM

Hi
I'm trying count how many times each ID number occurs in a list

eg
list
1
2
1
3
4
1
4

output
1 3
2 1
3 1
4 2

I've managed to do it (with some help) in Perl but am wondering if it is possible to do it in awk (which I understand better)?

One possible complication is that the list will form the first column of a datafile but that would be easily solved by awk '{print $1}' data > temp

Many thanks in advance
UnixKiwi

ghostdog74 · 11-27-2008, 10:49 PM

if you used Perl's hashes, you can do the same in awk using associative arrays

Code:

awk '{a[$1]++}END{for (i in a) print i,a[i]}' file

UnixKiwi · 11-27-2008, 11:16 PM

thanks for that, it works perfectly and is much simpler than the perl script I had

ta0kira · 11-28-2008, 04:02 AM

Do they have to stay in their original order?

Code:

sort | uniq | grep -n .

ta0kira

edit: Sorry, I was going off of the title of the thread and didn't pay enough attention to the other posts. You actually ask two separate questions!

Telemachos · 11-29-2008, 02:49 PM

Just for the record, this shouldn't be very hard using Perl:

Code:

#!/usr/bin/perl
use warnings;
use strict;

my %count;

while (<DATA>) {
  chomp;
  $count{$_} += 1;
}

foreach my $key (sort keys %count) {
  print "\t$key => $count{$key}\n";
}
__DATA__
1
2
1
3
4
1
4

Output

Code:

telemachus ~ $ perl count 
        1 => 3
        2 => 1
        3 => 1
        4 => 2