Online PHP editor | refs for Wv0nL

<?php $arr = array( 'key a' => array( 'key b' => 'element b', 'key c' => 'element c', 'key d' => array( 'key e' =>'element e' ), 'key f' => 'element f', 'key g' => 'element g' ), 'key h' => 'element h', 'key i' => array( 'key j' => 'element j', 'key k' => 'element k' ) ); function walk_recursive($arr, &$list = []) { foreach ($arr as $k => $ar) { if (is_array($ar)) { $list[] = $k; walk_recursive($ar, $list); } else { $list[] = $ar; } } return $list; } print_r(walk_recursive($arr));