Argument "*" isn't numeric in array element - perl

Question

I want to make a hash of array from a file that looks like:
xx500173:56QWER 45 A rtt34 34C
...
I would like to have a unique "key" (e.g. column1_column2)
#!/usr/bin/perl
use warnings;
use strict;
my $seq;
while(<>){
chomp;
my #line = split(/\s+/, $_);
my $key = $line[0] . "_" . $line[1]; #try to make a unique key for each entry
map { $seq->{ $_->[$key] } = [#$_[0..4]] } [ split/\s+/ ];
}
foreach my $s (keys %{$seq} ) {
print $s,": ",join( "\t", #{ $seq->{$s}} ) . "\n";
}
but I get the following error:
Argument "xx500173:56QWER_45" isn't numeric in array element
Does is it matter if key is numeric or string?

Answer 1

An index to an array [] should be numeric, but $key is not numeric. Assuming you want all the white-space-separated tokens as elements of your array:
use warnings;
use strict;
my $seq;
while (<DATA>) {
chomp;
my #line = split;
my $key = $line[0] . "_" . $line[1]; #try to make a unique key for each entry
$seq->{$key} = [ #line ];
}
foreach my $s ( keys %{$seq} ) {
print $s, ": ", join( "\t", #{ $seq->{$s} } ) . "\n";
}
__DATA__
xx500173:56QWER 45 A rtt34 34C
Outputs:
xx500173:56QWER_45: xx500173:56QWER 45 A rtt34 34C

Answer 2

You have confused yourself with the line
map { $seq->{ $_->[$key] } = [#$_[0..4]] } [ split/\s+/ ];
which is wrong because
map is an operator for translating one list into another by performing the same operation on every element of the input list, but you are ignoring the returned value
The input list is only one item long - the array reference returned by [ split/\s+/ ]
What you have written is the same as
$_ = [ split /\s+/ ];
$seq->{ $_->[$key] } = [ #$_[0..4] ];
and the problem is that $_->[$key] tries to index the anonymous array using the string $key, which is clearly wrong.
All you need here is
$seq->{$key} = [ #line[0..4] ];
and your complete program should look like this
#!/usr/bin/perl
use strict;
use warnings;
my $seq;
while ( <> ) {
chomp;
my #line = split;
$seq->{"$line[0]_$line[1]"} = [ #line[0..4] ];
}
for my $s ( keys %{$seq} ) {
printf "%s: %s\n", $s, join("\t", #{ $seq->{$s} } );
}