Perl: Searching for item in an Array

Question

Given an array @A we want to check if the element $B is in it. One way is to say this:

Foreach $element (@A){
    if($element eq $B){
        print "$B is in array A";
    }
}

However when it gets to Perl, I am thinking always about the most elegant way. And this is what I am thinking: Is there a way to find out if array A contains B if we convert A to a variable string and use

index(@A,$B)=>0

Is that possible?

Related: http://stackoverflow.com/questions/7898499/grep-to-find-item-in-perl-array http://stackoverflow.com/questions/3086874/find-the-item-in-an-array-that-meets-a-specific-criteria-if-there-is-one-perl — daxim, Apr 20 '12 at 07:06

score 13 · Accepted Answer · edited Apr 20 '12 at 07:41

13

There are many ways to find out whether the element is present in the array or not:

Using foreach

foreach my $element (@a) {
    if($element eq $b) {
       # do something             
       last;
    }
}

Using Grep:
```
my $found = grep { $_ eq $b } @a;
```

Using List::Util module

use List::Util qw(first); 

my $found = first { $_ eq $b } @a;

Using Hash initialised by a Slice

my %check;
@check{@a} = ();

my $found = exists $check{$b};

Using Hash initialised by map

my %check = map { $_ => 1 } @a;

my $found = $check{$b};

edited Apr 20 '12 at 07:41

bvr

9,687
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answered Apr 20 '12 at 05:49

Nikhil Jain

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The List::Util::first() example is (potentially) subtly incorrect when searching for false values, since `$found` will also evaluate false. (`die unless $found` ... oops!) [List::MoreUtils::any](http://search.cpan.org/perldoc?List::MoreUtils) does the right thing here. – pilcrow May 02 '12 at 19:56

score 6 · Answer 2 · answered Apr 20 '12 at 04:56

6

use 5.10.1;

$B ~~ @A and say '$B in @A';

answered Apr 20 '12 at 04:56

yazu

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You have to be very careful with this because this distributes the match over the elements. If @A has an array reference element that contains $B, this will still match even though $B isn't a top level element of @A. The smart match is fundamentally broken for this and many other reasons. – brian d foy Apr 20 '12 at 13:07

score 0 · Answer 3 · answered Apr 20 '12 at 05:51

0

use List::AllUtils qw/ any /;
print "\@A contains $B" if any { $B eq $_ } @A;

answered Apr 20 '12 at 05:51

obmib

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2

I would recommend `first` in this case, as it does not have to traverse whole array. It can stop when item is found. – bvr Apr 20 '12 at 07:43
any can stop too because it needs only one element to be true. – brian d foy Apr 20 '12 at 13:10
Beware that `first` can also return a false value if it finds, e.g., "0", which would confound the example given in this answer. `any` has the desired semantics. – pilcrow May 03 '12 at 01:38

Perl: Searching for item in an Array

3 Answers3