Why does it matter if your dog repeats? 
if($dog_hash{$dog_type}){
    print "dog [$dog_type] already in hash\n";
}else{
    $dog_hash{$dog_type} = $food_type;
}

[download]
I think that RazorbladeBidet's referral is probably the way to go if you really want to know how to hash well.

In reply to Re^2: Creating data structure from multiple pairs of information by Grundle
in thread Creating data structure from multiple pairs of information by tlemons

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