PHP flat array one dimension high and with empty values

Question

I have this array $data:

Array
(
  [0] => Array
      (
          [0] => 1
      )

  [1] => Array
      (
      )

  [2] => Array
      (
      )

  [3] => Array
      (
          [0] => test@email.net
      )

)

There are always only one element in each array. So, how can i transform the $data array to this? I need the empty values too:

Array
(
  [0] => 1
  [1] =>
  [2] =>
  [3] => test@email.net
)

Answer 1

Use array_map:

$arr = Array
(
  [0] => Array
      (
          [0] => 1
      )

  [1] => Array
      (
      )

  [2] => Array
      (
      )

  [3] => Array
      (
          [0] => test@email.net
      )

);

function flaten($n)
{
    if (isset($n[0])) {
       return $n[0];
    } else {
       return "";
    }
}

$resultArray = array_map(flaten, $arr);