Perl FAQ 5.5

There are several ways to approach this. If you are going to make this query many times and the values are arbitrary strings, the fastest way is probably to invert the original array and keep an associative array lying about whose keys are the first array's values.

    @blues = ('turquoise', 'teal', 'lapis lazuli');
    undef %is_blue;
    for (@blues) { $is_blue{$_} = 1; }

Now you can check whether $is_blue{$some_color}. It might have been a good idea to keep the blues all in an assoc array in the first place.

If the values are all small integers, you could use a simple indexed array. This kind of an array will take up less space:

    @primes = (2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31);
    undef @is_tiny_prime;
    for (@primes) { $is_tiny_prime[$_] = 1; }

Now you check whether $is_tiny_prime[$some_number].

If the values in question are integers instead of strings, you can save quite a lot of space by using bit strings instead:

    @articles = ( 1..10, 150..2000, 2017 );
    undef $read;
    grep (vec($read,$_,1) = 1, @articles);
    
    Now check whether vec($read,$n,1) is true for some $n.

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