array_diff

Compares array1 against one or more other arrays and returns the values in array1 that are not present in any of the other arrays.

The array to compare from

An array to compare against

More arrays to compare against

Returns an array containing all the entries from array1 that are not present in any of the other arrays.

Two elements are considered equal if and only if (string) $elem1 === (string) $elem2. In words: when the string representation is the same.

This function only checks one dimension of a n-dimensional array. Of course you can check deeper dimensions by using array_diff($array1[0], $array2[0]);.

<?php
$array1 = array("a" => "green", "red", "blue", "red");
$array2 = array("b" => "green", "yellow", "red");
$result = array_diff($array1, $array2);

print_r($result);
?>

Array
(
    [1] => blue
)

array_diff_assoc() -

array_intersect() -

array_intersect_assoc() -