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Answer: How to find out if X is an element in an array?

by Corion (Pope)
on Jun 27, 2000 at 18:29 UTC ( #20006=categorized answer: print w/replies, xml ) Need Help??

Q&A > arrays > How to find out if X is an element in an array? - Answer contributed by Corion

The other answers are all cool for arrays, but maybe using an array is wrong in the first place. Perl has a data type specialized for fast lookups, the hash (denoted by a % in front of the variable name). A lookup of an element in a hash is very fast, while grep and the likes have to go through the whole array, which is slower.

There are some drawbacks to hashes as well, first, they require you to change your code and second and more importantly, a hash dosen't preserve the order of elements - you can't get the elements back from the hash in the order you put them into the hash.

If the above drawbacks are no problem with you, you might want to use the following code :

#!/usr/bin/perl -w use strict; my %elements; my $element = "foo"; # Fill up our hash a bit foreach ("bla", "blubb", "foo", "bah") { $elements{$_} = 1; }; # now check if $element is in our hash : print "Found '$element'\n" if (exists $elements{$element}); print "D'oh - '$element' not found\n" unless (exists $elements{$elem +ent}); # You can still get to all elements in %elements : foreach (keys %elements) { # but they are in some weird order ... print "$_\n"; };

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