Nested array. Third level is disappearing

Question

I have that array :

$a = array(
    \"7\" => array(
        \"id\" => 7,
        \"parent\" => 6
    ),
    \"6\" => array(
        \"id\" =>         


        

Answer 1

Are you sure that output array is correct? Surely the key 2 should be a child of 1 (since 2 has 'parent'=>1)? If this is not the case, I don't understand what are actually trying to do and how the keys all relate to each other.

If 2 should be a child of 1, this works:

$keep = array();
foreach ($a as $k => &$v) {
  // Loop the array first time and create references to
  // structure the array how you want it
  if ($v['parent']) {
    $a[$v['parent']][0] = array($k => &$v);
  } else $keep[] = $k;
}

foreach ($a as $k => $v) {
  // Loop it again to get rid of non-root nodes from the root
  if (!in_array($k,$keep)) {
    unset($a[$k]);
  }
}

print_r($a);