array_diff_uassoc Computes the difference of arrays with additional index check which is performed by a user supplied callback function arrayarray_diff_uassoc arrayarray1 arrayarray2 array... callbackkey_compare_func array_diff_uassoc returns an array containing all the values from array1 that are not present in any of the other arguments. Note that the keys are used in the comparison unlike array_diff. This comparison is done by a user supplied callback function. It must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second. This is unlike array_diff_assoc where an internal function for comparing the indices is used. $b)? 1:-1; } $array1 = array("a" => "green", "b" => "brown", "c" => "blue", "red"); $array2 = array("a" => "green", "yellow", "red"); $result = array_diff_uassoc($array1, $array2, "key_compare_func"); ?> ]]> &example.outputs; brown [c] => blue [0] => red ) ]]> In our example above you see the "a" => "green" pair is present in both arrays and thus it is not in the ouput from the function. Unlike this, the pair 0 => "red" is in the ouput because in the second argument "red" has key which is 1. The equality of 2 indices is checked by the user supplied callback function. Please note that this function only checks one dimension of a n-dimensional array. Of course you can check deeper dimensions by using, for example, array_diff_uassoc($array1[0], $array2[0], "key_compare_func");. See also array_diff, array_diff_assoc, array_udiff, array_udiff_assoc, array_udiff_uassoc, array_intersect, array_intersect_assoc, array_uintersect, array_uintersect_assoc and array_uintersect_uassoc.