note 24684 modified in function.array-fill by felipe

array_fill() cannot be used to setup only missing keys in an array. This  may be necessary for example before using implode()  on a sparse filled array.
The solution is to use this function:

<?php
function array_setkeys(&$array, $fill = NULL) {
  $indexmax = -1;
  for (end($array); $key = key($array); prev($array)) {
    if ($key > $indexmax)
      $indexmax = $key;
  }
  for ($i = 0; $i <= $indexmax; $i++) {
    if (!isset($array[$i]))
      $array[$i] = $fill;
  }
  ksort($array);
}
?>

This is usefull in some situations where you don't know which key index was filled and you want to preserve the association between a positioned field in an imploded array and the key index when exploding it.

--was--
array_fill() cannot be used to setup only missing keys in an array. This  may be necessary for example before using implode()  on a sparse filled array.
The solution is to use this function:

<?php
function array_setkeys(&$array, $fill = NULL) {
  $indexmax = -1;
  for (end($array); $key = key($array); prev($array)) {
    if ($key > $indexmax)
      $indexmax = $key;
  }
  for ($i = 0; $i <= $indexmax; $i++) {
    if (!isset($array[$i]))
      $array[$i] = $fill;
  }
  ksort($array);
}
?>

This is usefull in some situations where you don't know which key index was filled and you want to preserve the association between a positioned field in an imploded array and the key index when exploding it.

http://php.net/manual/en/function.array-fill.php