Converting an array from one to multi-dimensional based on parent ID values

Question

I\'ve got a one-dimensional array of objects that represent multi-dimensional data:

array(
    array(
        \"id\" => 45,
        \"parent_id\" => nu         


        

Answer 1

function convertArray ($array) {
  // First, convert the array so that the keys match the ids
  $reKeyed = array();
  foreach ($array as $item) {
    $reKeyed[(int) $item['id']] = $item;
  }
  // Next, use references to associate children with parents
  foreach ($reKeyed as $id => $item) {
    if (isset($item['parent_id'], $reKeyed[(int) $item['parent_id']])) {
      $reKeyed[(int) $item['parent_id']]['children'][] =& $reKeyed[$id];
    }
  }
  // Finally, go through and remove children from the outer level
  foreach ($reKeyed as $id => $item) {
    if (isset($item['parent_id'])) {
      unset($reKeyed[$id]);
    }
  }
  return $reKeyed;
}

I feel sure this can be reduced to only two loops (combining the second and third) but right now I can't for the life of me figure out how...

NOTE This function relies on parent_id for items with no parent being either NULL or not set at all, so that isset() returns FALSE in the last loop.