while (){ chomp; my @line = split ('\t', $_); my $key1 = 'A' . $line[0] . '.' . 'A' . $line[1]; ##first key my $key2 = 'A' . $line[1] . '.' . 'A' . $line[0]; ##key the other way ##check to see if the key exists in the hash ##if it doesn't there is data in your infile, not in you names array ##new logic if($line[0] <= $line[1]) { if(exists $diplotypes{$key1}) { $diplotypes{$key1} += $line[2]; } else { #key doesnt exist so add it $diplotypes{$key1} = $line[2]; } } else { if(exists $diplotypes{$key2}) { $diplotypes{$key2} += $line[2]; } else { #key doesnt exist so add it $diplotypes{$key2} = $line[2]; } } }}