php Convert multidimensional array into single array

$singleArray = []; 
foreach ($parentArray as $childArray) 
{ 
    foreach ($childArray as $value) 
    { 
    $singleArray[] = $value; 
    } 
}

function array_flatten($array) { 
  if (!is_array($array)) { 
    return FALSE; 
  } 
  $result = array(); 
  foreach ($array as $key => $value) { 
    if (is_array($value)) { 
      $result = array_merge($result, array_flatten($value)); 
    } 
    else { 
      $result[$key] = $value; 
    } 
  } 
  return $result; 
}