my $result = { 'A' => { 1 => 1, 2 => 1, 7 => 1, 10 => 1, ... }, 'B' => { ... }, ... }; #### open my $fh, '<', $filename; while (<$fh>) { chomp; my ($id, @numbers) = split; for my $number (@numbers) { $result->{$id}{$number} = 1; } } #### my %unique_numbers = (); for (values %$result) { for my $number (keys %$_) { $unique_numbers{$number} = 1; } } my @numbers = sort {$a <=> $b} keys %unique_numbers; open my $out_fh, '>', $output_filename; print $out_fh "IDs @numbers\n"; for my $id (sort keys %$result) { my @fields = $id; for my $number (@numbers) { if (exists $result->{$id}{$number}) { push @fields, 1; } else { push @fields, 0; } } my $string = join " ", @fields; print $out_fh "$string\n"; }