Determining if an element is already in an array.

ithron has asked for the wisdom of the Perl Monks concerning the following question:

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RE: Determining if an element is already in an array. by davorg (Chancellor) on Feb 02, 2000 at 01:17 UTC
No need for a loop. Try this: `my %check; @check{@arr) = (1) x @arr;` [download] You now have a hash `%check` which has a key/value pair for each element in the list. You can check for the existance of value, `$val`, by doing: `if $check{$val}` [download]	[reply] [d/l] [select]
Re: Determining if an element is already in an array. by Anonymous Monk on Feb 02, 2000 at 00:04 UTC
You can use the grep function: push(@foo,$elm) unless grep(/$elm/,@foo); Creating a hashtable every time you're tring to test for an element may be alot of overhead (memory and CPU).	[reply]
Re: Determining if an element is already in an array. by dlc (Acolyte) on Feb 01, 2000 at 21:45 UTC
the foreach loop is not so convoluted. i spell if f-o-r here. `my @foo = qw(1 4 g 7 h rf s 4 6 7 9); my %foo = (); $foo{$_}=$foo[$_] for @foo; @foo=keys %foo;` [download] @foo is your original list, and %foo is a temporary hash that you will use to hold the unique values (since every key in a hash is unique).	[reply] [d/l]
Re: Determining if an element is already in an array. by Anonymous Monk on Feb 02, 2000 at 18:23 UTC
I'm sort of new to this, so maybe this is just 'baby talk', but this has always worked for me: push @arr, $el if !$seen{$el}++; The hash value $seen{$el} is not incremented until after the test and so is always zero the first time through, non-zero thereafter.	[reply]