One thing I see is that $hash_ref seems to be constant, so you can compute the list of keys once instead of each time: @keys = keys %$hash_ref; and for my $key (@keys)

And if several $a values can share $b sub values, you can keep the subsums in cache to avoid recomputing them (untested because you didn't provide sample data): 

use List::Util qw( sum );
my %cache;
my @keys = keys %$hash_ref;
foreach my $a_ (@{ $array_ref }) {
    my $i = 0;
    foreach my $b_ (split('-', $a_)) {
        $i += $cache{$b_} //= sum map { $_->{value} } @{ $foo->{$b_} }
+{@keys}; # Use the cached value or compute the sum
    }
    push @{ $bar->{$i} }, $a_;
}

[download]
Using the orcish manoeuver, List::Util, and a slice

I suppose the name are only because this is an example? Even in a example I would avoid $a and $b, (even more so when using List::Util) because of their special meaning. (Edit) And I avoid single char names as a general rule

Edit $hash_ref->{$b_ } should have been $foo->{$b_}. Thanks kcott

In reply to Re: Optimize a perl block by Eily
in thread Optimize a perl block by IruP

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