I undef @arr_2_hash{@arr_2}; in sub hash_grep(), noting it was faster than the OP's original.

Changing this @diff3{@arr_1} = @arr_1; to @diff3{@arr_1} = () makes some difference.

No--it makes a huge difference and it, by far, blows everything else away. Will make that change in a new sub and re-benchmark. Glad you mentioned it!

In reply to Re^3: Best method to diff very large array efficiently by Kenosis
in thread Best method to diff very large array efficiently by newbieperlperson

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