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<?php $arr = array(); $a = [0,1,2,3,4,5]; $b = [0,1,2,3,4,5]; $c = [0,1,2,3,4,5]; $d = [0,1,2,3,4,5]; $e = [0,1,2,3,4,5]; $f = [0,1,2,3,4,5]; $g = [0,1,2,3,4,5]; $arr[] = $a; $arr[] = $b; $arr[] = $c; $arr[0][2] = $d; $arr[0][2][3] = $e; $arr[2][1] = $f; $arr[1] = $g; print_r($arr); function array_keys_recur($array) { if(!is_array($array)) return false; $keys = array_keys($array); foreach($keys as $k => $key) { $keys[$k] = array_keys_recur($key); } return $keys; } $keys = array_keys_recur($arr); print_r($keys);