CODEWITHSUNDEEP
phparrayssequence
Jonas Lindeløv
Jonas Lindeløv

Reputation: 5683

PHP: Detecting a particular sequence of elements in an array

How do I detect if a certan sequence of elements is present in an array? E.g. if I have the arrays and needle

$needle = array(1,1);
$haystack1 = array(0,1,0,0,0,1,1,0,1,0);
$haystack2 = array(0,0,0,0,1,0,1,0,0,1);

How does one detect if the subset $needle is present in e.g. $haystack1? This method should return TRUE for $haystack1 and FALSE for $haystack2.

Thanks for any suggestions!

Upvotes: 3

Views: 847

Answers (3)

Jon
Jon

Reputation: 437424

For the specific case where no array element is a prefix of any other element (when both are converted to strings) then the already posted answers will work fine and probably be pretty fast.

Here's an approach that will work correctly in the general case:

function subarray_exists(array $needle, array $haystack) {
    if (count($needle) > count($haystack)) {
        return false;
    }

    $needle = array_values($needle);
    $iterations = count($haystack) - count($needle) + 1;
    for ($i = 0; $i < $iterations; ++$i) {
        if (array_slice($haystack, $i, count($needle)) == $needle) {
            return true;
        }
    }

    return false;
}

See it in action.

Disclaimer: There are ways to write this function that I expect will make it execute much faster when you are searching huge haystacks, but for a first approach simple is good.

Upvotes: 3

Sampson
Sampson

Reputation: 268364

Join the arrays, and check for the strpos of the needle.

if ( strpos( join($haystack1), join($needle) ) >= 0 ) {
    echo "Items found";
}

Demo: http://codepad.org/F13DLWOI

Warning

This will not work for complicated items like objects or arrays within the haystack array. This method is best used with itesm like numbers and strings.

Upvotes: 6

Ignacio Vazquez-Abrams
Ignacio Vazquez-Abrams

Reputation: 798754

If they're always a single digit/character then you can convert all elements to strings, join by '', and use the regex or string functions to search.

Upvotes: 3

Related Questions