Rajiv has asked for the wisdom of the Perl Monks concerning the following question: ⭐ (hashes)

I want to find the union of two hashes. I tried the option of merging the two hashes, but found that relatively slower. Can anybody suggest me a good optimized code for getting the union of two hashes. The option that i am trying looks like this: 
foreach $k (sort keys %hash1) {
  if (exists($hash2{$k})) {
     $matchWords++;
   } 
}

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This snippet runs faster than merging. I don't understand how ??

Originally posted as a Categorized Question.

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Re: Union of Two Hashes⭐
by maverick (Curate) on Apr 09, 2002 at 14:35 UTC
    The question is a bit confusing...you ask for a union, but you code snippet looks like you're looking for the intersection. Union first. For small hashes this is really quick: 
    %union = (%first, %second);

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    For large: 
    while (($k,$v) = each %first) { $union{$k} = $v; }
while (($k,$v) = each %second) { $union{$k} = $v; }

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    (makes sense once you consider the memory usage for the first snippet.

    For intersection, all you really need to do is change $matchWords to $matchWords{$k}++ the iterate of then matchWords looking for values == 2

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