Checking if array is multidimensional or not?

Question

1. What is the most efficient way to check if an array is a flat array of primitive values or if it is a multidimensional array?

Answer 1

$is_multi_array = array_reduce(array_keys($arr), function ($carry, $key) use ($arr) { return $carry && is_array($arr[$key]); }, true);

Here is a nice one liner. It iterates over every key to check if the value at that key is an array. This will ensure true