PHP Manual: array_diff

Description

array array_diff_ukey ( array array1, array array2 [, array ..., callback key_compare_func] )

array_diff_ukey() returns an array containing all the values of array1 that have keys that are not present in any of the other arguments. Note that the associativity is preserved. This function is like array_diff() except the comparison is done on the keys instead of the values.

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 key is considered to be respectively less than, equal to, or greater than the second.

Example 1. array_diff_ukey() example

<?php
function key_compare_func($key1, $key2)
{
    if ($key1 == $key2)
        return 0;
    else if ($key1 > $key2)
        return 1;
    else
        return -1;
}

$array1 = array('blue'  => 1, 'red'  => 2, 'green'  => 3, 'purple' => 4);
$array2 = array('green' => 5, 'blue' => 6, 'yellow' => 7, 'cyan'   => 8);

var_dump(array_diff_ukey($array1, $array2, 'key_compare_func'));
?>

The above example will output:

array(2) {
  ["red"]=>
  int(2)
  ["purple"]=>
  int(4)
}

Note: Please note that this function only checks one dimension of a n-dimensional array. Of course you can check deeper dimensions by using array_diff_ukey($array1[0], $array2[0], 'callback_func');.