Online PHP editor | refs for 1brJs

<?php $tree = array( 1 => array( 'parent_id' => null, 'name' => 'root', 'depth' => 0, ), 11 => array( 'parent_id' => 1, 'name' => 'a', 'depth' => 1, ), 12 => array( 'parent_id' => 1, 'name' => 'b', 'depth' => 1, ), 111 => array( 'parent_id' => 11, 'name' => 'aa', 'depth' => 2, ), 2 => array( 'parent_id' => null, 'name' => 'other root', 'depth' => 0, ) ); foreach ($tree as $key => &$sub) { if (isset($sub['parent_id'])) { $tree[$sub['parent_id']]['children'][$key] = &$sub; } } unset($sub); // unset the reference to make sure to not overwrite it later... // now remove the entries with parents foreach ($tree as $key => $sub) { if (isset($sub['parent_id'])) unset($tree[$key]); } var_dump($tree);