Online PHP editor | output for KcqV0

<?php function gen() { $data = array(); $i = 0; for($i; $i < 50; $i++) { $data[$i] = array( 'indent' => 'test ' . $i, 'depth' => 1 ); } return array(); } echo serialize(gen()); /* $array = array( 55 => array( 'ident' => 'test 1', 'depth' => 1, ), 77 => array( 'parent_id' => 55, 'ident' => 'test 2', 'depth' => 2, ), 109 => array( 'parent_id' => 77, 'ident' => 'test 3', 'depth' => 3, ), 78 => array( 'parent_id' => 55, 'ident' => 'test 4', 'depth' => 2, ), 25 => array( 'ident' => 'test 5', 'depth' => 1, ) ); */ $array = unserialize('a:0:{}'); /* function v1($array) { foreach ($array as $key => &$sub) { if (isset($sub['parent_id'])) { $array[$sub['parent_id']]['children'][$key] = &$sub; } } unset($sub); // unset the reference to make sure to not overwrite it later... // now remove the entries with parents foreach ($array as $key => $sub) { if (isset($sub['parent_id'])) unset($array[$key]); } return $array; } function push_at_key($what, $what_key, $key, $array) { foreach($array as $k => $v) { if($key == $k) { $array[$k]['children'][$what_key] = $what; return $array; } } foreach($array as $k => $v) { $array[$k] = push_at_key($what, $what_key, $key, $v['children']); } return $array; } function v2($array) { $out = array(); foreach ($array as $key => $sub) { if(!isset($sub['parent_id'])) { $out[$key] = $sub; } else { $out = push_at_key($sub, $key, $sub['parent_id'], $out); } } return $out; } //var_dump(v1($array)); //var_dump(v2($array)); */