In Perl, how do I create a hash whose keys come from a given array?

arrays perl hash
raldi picture raldi · Sep 18, 2008 · Viewed 124.4k times · Source

Let's say I have an array, and I know I'm going to be doing a lot of "Does the array contain X?" checks. The efficient way to do this is to turn that array into a hash, where the keys are the array's elements, and then you can just say 

if($hash{X}) { ... }

Is there an easy way to do this array-to-hash conversion? Ideally, it should be versatile enough to take an anonymous array and return an anonymous hash.

Answer

raldi picture raldi · Sep 18, 2008 
%hash = map { $_ => 1 } @array;

It's not as short as the "@hash{@array} = ..." solutions, but those ones require the hash and array to already be defined somewhere else, whereas this one can take an anonymous array and return an anonymous hash.

What this does is take each element in the array and pair it up with a "1". When this list of (key, 1, key, 1, key 1) pairs get assigned to a hash, the odd-numbered ones become the hash's keys, and the even-numbered ones become the respective values.

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