php: compute differences (inserts, updates, deletes) between two associative arrays

get_array_differences

<?php

/**
 * compute differences between associative arrays.
 * the inserts, updates, deletes are returned
 * in separate arrays. Note: To combine arrays
 * safely preserving numeric keys, use $a + $b
 * instead of array_merge($a, $b).
 *
 * Author: Monte Ohrt <monte@ohrt.com>
 * Version: 1.0
 * Date: July 17th, 2014
 *
 * @param array $a1
 * @param array $a2
 * @return array ($inserts, $updates, $deletes)
 */
get_array_differences($a1, $a2) {
    // get diffs forward and backward
    $forward = array_diff_assoc($a1, $a2);
    $backward = array_diff_assoc($a2, $a1);
    // compute arrays
    $inserts = array_diff_key($forward, $backward);
    $updates = array_intersect_key($forward, $backward);
    $deletes = array_diff_key($backward, $forward);
    return array($inserts, $updates, $deletes);
}