I personally like the hash of arrays approach, as it more closely mirrors the way I think about the problem: a key (IP address) that can have one or more aliases. However, as I noted in my original post, it is not the most efficient way to do things...just a bit easier to understand for a beginner IMHO.

I understand what you're saying, but I'd go in a different direction.

If a beginner understands AoA:

$array[$row][$col] = $pixel;
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and that hashes are sort of arrays with different brackets:

$array{$row}{$col} = $pixel;
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then it's a small leap to suggest that (here, at least) the keys are the interesting bits, and the values don't matter:

$hosts{$ip}{$alias} = 1;
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