Multidimensional PHP array – Key exists

I want a function that will return TRUE or FALSE based on if a given key exists in a multidimensional array in PHP.

I haven’t been able to figure out a recursive function to perform this action.

A sample of what this could do:

$array = array(
    'key 1' => array(
        'key 1.1' => array()
        'key 1.2' => array()
    ),
    'key 2' => array(
        'key 2.1' => array(
            'key 2.1.1' => array()
        )
        'key 2.2' => array()
    )
);

multi_array_key_exists('key 1', $array); // return TRUE

multi_array_key_exists('key 2.1.1', $array); // return TRUE

multi_array_key_exists('key 3', $array); // return FALSE

Answer

This is where a recursive function comes in handy.

function multi_array_key_exists($key, array $array): bool
{
    if (array_key_exists($key, $array)) {
        return true;
    } else {
        foreach ($array as $nested) {
            if (is_array($nested) && multi_array_key_exists($key, $nested))
                return true;
        }
    }
    return false;
}

Note that this can take some time (in long nested arrays), it might be better to flatten first, since you are only interested in whether the key exists or not.