Sorting an array into a multidimensional array based on “parent_id”

Question

I\'m storing an infinitely nested directory structure in mysql by assigning a \"parent_album_id\" to each \"album\" (unless it\'s at the top level, in which case it does not hav

Answer 1

// you already managed to get the array into this form
$albums = array(
  1 => array('id'=>1, 'title'=>'Album 1', 'parentId'=>null),
  2 => array('id'=>2, 'title'=>'Album 2', 'parentId'=>null),
  3 => array('id'=>3, 'title'=>'Album 1.1', 'parentId'=>1),
  4 => array('id'=>4, 'title'=>'Album 1.1.1', 'parentId'=>3),
  5 => array('id'=>5, 'title'=>'Album 2.1', 'parentId'=>2),
  6 => array('id'=>6, 'title'=>'Album 1.1.2', 'parentId'=>3),
  7 => array('id'=>7, 'title'=>'Album 1.1.3', 'parentId'=>3)
);

print_r(foo($albums));


function foo($albums) {
  $rv = array();
  foreach( $albums as &$album) {
    if ( is_null($album['parentId']) ) {
      // no parentId -> entry in the root array
      $rv[] = &$album;
    }
    else {
      $pid = $album['parentId'];
      if ( !isset($albums[$pid]) ) {
        echo 'orphant album: ', $album['id'], "\n";
      }
      else {
        if ( !isset($albums[$pid]['children']) ) {
          $albums[$pid]['children'] = array();
        }
        $albums[$pid]['children'][] = &$album;
      }
    }
  }
  return $rv;
}

prints

Array
(
  [0] => Array
    (
    [id] => 1
    [title] => Album 1
    [parentId] => 
    [children] => Array
      (
        [0] => Array
        (
          [id] => 3
          [title] => Album 1.1
          [parentId] => 1
          [children] => Array
            (
            [0] => Array
              (
                [id] => 4
                [title] => Album 1.1.1
                [parentId] => 3
              )

            [1] => Array
              (
                [id] => 6
                [title] => Album 1.1.2
                [parentId] => 3
              )

            [2] => Array
              (
                [id] => 7
                [title] => Album 1.1.3
                [parentId] => 3
              )

            )

        )

      )

    )

  [1] => Array
    (
    [id] => 2
    [title] => Album 2
    [parentId] => 
    [children] => Array
      (
        [0] => Array
        (
          [id] => 5
          [title] => Album 2.1
          [parentId] => 2
        )

      )

    )

)