How to check if an array contains another array in PHP?

Question

I would have a rather simple question today. We have the following resource:

$a = array(1 => 5, 2 => 3, 3 => 13, 9 => array('test'), 4 => 32, 5 => 33);

How is it actually possible to find out if array "a" has an array element in it and return the key if there is one (or more)?

Answer 1

One possible approach:

function look_for_array(array $test_var) {
  foreach ($test_var as $key => $el) {
    if (is_array($el)) {
      return $key;
    }
  }
  return null;
}

It's rather trivial to convert this function into collecting all such keys:

function look_for_all_arrays(array $test_var) {
  $keys = [];
  foreach ($test_var as $key => $el) {
    if (is_array($el)) {
      $keys[] = $key;
    }
  }
  return $keys;
}

Demo.