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Union of Two Hashes

( #157715=categorized question: print w/ replies, xml ) Need Help??
Contributed by Rajiv on Apr 09, 2002 at 13:37 UTC
Q&A  > hashes


Description:

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

Answer: Union of Two Hashes
contributed by maverick

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