my $file_number = 0;

# loop through all file-handles
foreach my $file (@files) {

        # open the file
        open(my $fh, '<', $file) or croak "Unable to open file: $file";

        # count this file as being processed
        ++$file_number;

        # give the user a little bit of an update
        print "Now processing file $file_number\n";

        # completely process the file
        while (<$fh>) {

                # trim leading/trailing whitespace
                s/^\s+//;
                s/\s+$//;

                # tab-delimited rows with the stats value in the last column
                my @row = split("\t");
                my $val = pop(@row);

                # sort the row and concatenate it into a key
                @row = sort(@row);
                my $key = join("\t", @row);

                # skip rows with missing values
                next() if (scalar(@row) != $subset_num);

                # save this data point
                push @{ $data{$key} }, $val;

                }

        # look for any missing values
        foreach my $key (keys(%data)) {
                if ($file_number > scalar( @{ $data{$key} } )) {
                        push @{ $data{$key} }, '';
                        }
                }

        # close the filehandle
        close($fh);

        }