Question

I’m a perl newbie. I have a code in which a variable is loaded with several values during a foreach loop. What I want to do is to perform some operation on that variable only if its in that array. What is the most efficient way to do this in perl as the data I am working on is very large.

A simple example of my question is, say I have an array of fruits I want

@fruits_i_like = qw (mango banana apple);

But I have a $fruit variable in a foreach loop which gets the name of fruits from a data file that has all different types of fruits. How would I pick only those cases of $fruit that are in my @fruits_i_like array?

Answer 1

You can use a hash like this :

my %h = map {$_ => 1 } @fruits_i_like;
if (exists $h{$this_fruit}) {
    # do stuff
}

Here is a benchmark that compare this way vs mfontani solution

#!/usr/bin/perl 
use warnings;
use strict;
use Benchmark qw(:all);

my @fruits_i_like = qw/mango banana apple/;
my $this_fruit = 'banana';
my %h = map {$_ => 1 } @fruits_i_like;
my $count = -3;
my $r = cmpthese($count, {
    'grep' => sub {
         if ( scalar grep $this_fruit eq $_, @fruits_i_like ) {
             # do stuff
         }
    },
    'hash' => sub {
        if (exists $h{$this_fruit}) {
             # do stuff
        }
    },
});

Output:

          Rate grep hash
grep 1074911/s   -- -76%
hash 4392945/s 309%   --