jaydstein:

If you're trying to determine the category of a particular item, and you're doing it frequently in your code, then you might want to use a reverse lookup table (inverted hash). Basically, it's just a hash where each value points to the category name in your list:

$ cat 952190.pl
#!/usr/bin/perl
use strict;
use warnings;

my $hash = {
    'COOKIES'   => ['CHOCOLATE CHIP', 'PEANUT BUTTER', 'OATMEAL'],
    'METALS'    => ['SILVER', 'GOLD', 'PLATINUM'],
    'BREAKFAST' => ['OATMEAL', 'WAFFLES', 'CEREAL'],
};

my $values = {
    'COOKIES' => '1',
    'SILVER'  => '1',
};

my $revLookup;
for my $k (%$hash) {
    for my $v (@{$$hash{$k}}) {
        $$revLookup{$v} = $k;
    }
}

print who_do_ya_love('CHOCOLATE CHIP');
print who_do_ya_love('PLATINUM');
print who_do_ya_love('OATMEAL');

sub who_do_ya_love {
    my $item = shift;
    my $category = $$revLookup{$item} // 'NOTHING';
    "This guy loves $category\n";
}

$ perl 952190.pl
This guy loves COOKIES
This guy loves METALS
This guy loves BREAKFAST
[download]

The downsides of using an inverted hash:

• You actually have to build the inverted hash: That can be expensive for large quantities of data.
• Each time your list of values changes, you have to build it again--or add code to maintain the reverse hash with the rest of the data.
• Since values may be in multiple lists, you'll have to either:
  • (a) bear with it (as I did in this example), or
  • (b) decide how to handle (and then write code for) multiple lists.

...roboticus

When your only tool is a hammer, all problems look like your thumb.