map filter php

1<?php
2
3$arr = array(
4   "one" => array(1, 2),
5   "two" => array(1, 2),
6   "three" => array(1, 2)
7);
8$res = array();
9
10array_walk($arr, function ($v, $k) use (&$res) {
11    $res[$k] = $v[0];
12});
13
14print_r($res);