Modify key if it already exists - perl

Question

I'm writing a piece of code that creates a HoAs and loops through for each key. The snippet below shows a basic example of the problem I'm having.
#!/usr/bin/perl
use strict;
use warnings;
my #array1 = qw (1 1 3 4 5); # Note that '1' appears twice
my #array2 = qw (a b c d e);
my #array3 = qw (6 7 8 9 10);
my #array4 = qw (f g h i j);
my %hash;
push #{$hash{$array1[$_]}}, [ $array2[$_], $array3[$_], $array4[$_] ] for 0 .. $#array1;
for my $key (sort keys %hash) {
my ($array2, $array3, $array4) = #{$hash{$key}[-1]};
print "[$key] $array2\t$array3\t$array4\n";
}
Output:
[1] b 7 g
[3] c 8 h
[4] d 9 i
[5] e 10 j
For the data I'm actually using (as opposed to this example) I have been using a key that I've just realised isn't unique, so, as above I end up overriding non-uniqe keys. I'm mainly using these values as keys in order to sort by them later.
My question is either:
A) I can perform the above task for each key unless (exists $hash{$array1}) in which case I can modify it
or
B) Is there a way to sort by those values, in which case I could use another, non-redundant key.
Thanks!

Answer 1

so, as above I end up overriding non-uniqe keys
You aren't. Let's print out the whole contents of that hash:
for my $key (sort { $a <=> $b } keys %hash) { # sort numerically!
for my $array (#{ $hash{$key} }) { # loop over all instead of $hash{$key}[-1] only
say "[$key] " . join "\t", #$array;
}
}
Output:
[1] a 6 f
[1] b 7 g
[3] c 8 h
[4] d 9 i
[5] e 10 j
You would be overriding the values if you were building the hash like
$hash{$array1[$_]} = [ $array2[$_], $array3[$_], $array4[$_] ] for 0 .. $#array1;
(And printing it as)
for my $key ( ... ) {
say "[$key] " . join "\t", #{ $hash{$key} };
}
That is, assigning instead of pushing.
If you want to keep the first value assigned to each key, use the //= operator (assign if undef).