for my $col_num (1..$#counts) {         # for my $col_num (0, 8) { ??
   my $col_counts = $counts[$col_num];

   say("column ", $col_num+2);

   my %by_count;
   for keys(%$col_counts) {
      my $count = $col_counts->{$_};
      push @{ $by_count{$count} }, $_;
   }

   say
      join ' ',
         map { join(',', @{ $by_count{$_} }) }
            keys(%by_count);
}