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 have a parent_album_id).

I first grab an array of all the albums from the database and change each albums key to it's "id" (autoincrement id).

Next, I want to reorganize the array of albums into a multidemensional array, storing child albums in 'children' for each album. I've had some success. The following code works fine if I only need to go down one level in the array, but if I go down more than one level it loses the full structure of the array. This is because when I recursively call array_search_key I don't pass the full array, just the next level that I want to search.

How can I recursively search through the array, but return the entire multidimensional array of albums?

foreach ($albums as &$album){
    if($album['parent_album_id']){ // Move album if it has a parent
        $insert_album = $album;
        unset($albums[$album['id']]); // Remove album from the array, since we are going to insert it into its parent
        $results = array_search_key($album['parent_album_id'],$albums,$insert_album, $albums);
        if($results){
            $albums = $results;
        }
    }
}

function array_search_key( $needle_key, $array , $insert_album) {
   foreach($array AS $key=>&$value){
       if($key == $needle_key) {
           $array[$key]['children'][$insert_album['id']] = $insert_album;
           return $array;
       }
       if(is_array($value) && is_array($value['children'])){    
           if( ($result = array_search_key($needle_key, $value['children'], $insert_album)) !== false)
           return $result;
       }
   }
   return false;
}

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
        )

      )

    )

)