Every array element for the lookup will need to be hashed anyway, either for "storage" as a hash key or for lookup as a hash key, so that is a wash.

I usually choose the smaller array for the hash because the smaller array is more likely to fit in memory.

In reply to Re^3: Fastest way to merge (and de-dup) two large arrays? by Corion
in thread Fastest way to merge (and de-dup) two large arrays? by technojosh

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