my %error_per_file;
my %error_type;

while(my ($filename, $errnum) = get_row_elements($some,$params,$here)) {
    $error_type{$errnum}++;
    $error_per_file{$filename}->{$errnum}++;
}

##</code><code>##

my $column = 1;
my %column_for = map ($_ => $column++), sort keys %error_type;
$column_for{Filename} = 0;


##</code><code>##

$worksheet->write(0, $column_for{$col_name}, $col_name) for keys %column_for;


##</code><code>##

my $row = 1;
for my $filename (sort keys %error_per_file){
    $worksheet->write($row, 0, $filename)
    my ($errnum, $occurences);
    $worksheet->write($row, $column_for{$errnum}, $occurences)
        while ($errnum, $occurences) = each %{$error_per_file{$filename}};
    ++$row;
}