Use a hash to count the number of occurances of each id in @array2, like this:

my %count;
foreach (@array2) {
  my ($id) = split /,/;
  $count{$id}++;
}

foreach (sort @array2) {
  my ($id) = split /,/;
  print "$id: $count{$id}\n";
}
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If some of the ids in @array1 don't appear in @array2 then you'll need to account for that in the second loop.

But, all in all, I think you should probably rethink your data structure.

--
<http://www.dave.org.uk>

"Perl makes the fun jobs fun
and the boring jobs bearable" - me