With the nested approach he can also use things like keys %{$hash{$store}} to list all products.

If the OP doesn't need it, then no need to do it that way. We have no way of knowing if that's what the OP needs, maybe they don't know about the other solution. It's much more memory efficient than nested hashes, so is better when you don't need the nested hashes. It's best to know the pros and cons of both ways. I used the alternate solution just the other day to store 100,000's of what would have been nested several layers deep hashes, and I did not need to use keys or values or each. I just needed a quick lookup for a group of several different values.

The delimiter approach is a nice idea, but is neither shorter to write nor more efficient.

Also, this:

$hash{$product,$code} = 1;

[download]
Is very slightly shorter than this:
$hash{$product}{$code} = 1;

[download]

And the first requires only one hash lookup, while the second requires two. Not to micro-optimize or anything though...(and I'm not going to bother benchmarking the difference between joining two strings and looking up a hash value...at least not today, anyway)

In reply to Re^5: Possible for Map to create Hash of Hash? by runrig
in thread Possible for Map to create Hash of Hash? by konnjuta

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