perl, comparing hashes, sub set

Question

I was wondering if there is any easy algorithms to compare to see if one hash is a subset of another hash.

For example, if

$HASH{A} = B;
$HASH{B} = C;
$HASH{C} = D;

$HASH2{A} = B;
$HASH2{B} = C;

then %HASH2 is a subset of %HASH.

Answer 1

This uses "smart matching" (~~) and List::Util::first

use 5.010;
use List::Util qw<first>;

sub hash_is_subset { 
    my ( $hash, $cand ) = @_;
    return not defined( first { not $hash->{ $_ } ~~ $cand->{ $_ } } keys %$cand );
}

hash_is_subset( \%HASH, \%HASH2 );