In general, either a brute-force search which uses a loop of some kind, whether foreach, while, map, grep, etc. that checks each one until you find it; or

Create an index with the thing you are looking up as the hash key. In this case, loop over all the entries once, building another hash such that $index{string}=key2. Then reference that index as many times as needed, quickly.

If the reverse mapping is not unique, than things are more difficult, but you get the idea.

In reply to Re: fast hash search by John M. Dlugosz
in thread fast hash search by ddoc

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