PHP best way to MD5 multi-dimensional array?

Question

What is the best way to generate an MD5 (or any other hash) of a multi-dimensional array?

I could easily write a loop which would traverse through each level of the

Answer 1

Currently the most up-voted answer md5(serialize($array)); doesn't work well with objects.

Consider code:

 $a = array(new \stdClass());
 $b = array(new \stdClass());

Even though arrays are different (they contain different objects), they have same hash when using md5(serialize($array));. So your hash is useless!

To avoid that problem, you can replace objects with result of spl_object_hash() before serializing. You also should do it recursively if your array has multiple levels.

Code below also sorts arrays by keys, as dotancohen have suggested.

function replaceObjectsWithHashes(array $array)
{
    foreach ($array as &$value) {
        if (is_array($value)) {
            $value = $this->replaceObjectsInArrayWithHashes($value);
        } elseif (is_object($value)) {
            $value = spl_object_hash($value);
        }
    }
    ksort($array);
    return $array;
}

Now you can use md5(serialize(replaceObjectsWithHashes($array))).

(Note that the array in PHP is value type. So replaceObjectsWithHashes function DO NOT change original array.)