PHP递归统计不规则数组的总条数

首先我有这样一个数组

Array
(
    [id] => 4
    [name] => 衬衫
    [parent_id] => 0
    [sort] => 99
    [is_show] => 0
    [seller_id] => 0
    [part_img] => 
    [create_time] => 2018-06-27 15:20:39
    [update_time] => 2018-06-27 15:20:39
    [status] => 0
    [son] => Array
        (
            [5] => Array
                (
                    [id] => 5
                    [name] => 版型
                    [parent_id] => 4
                    [sort] => 99
                    [is_show] => 0
                    [seller_id] => 0
                    [part_img] => 
                    [create_time] => 2018-06-27 15:20:39
                    [update_time] => 2018-06-27 15:20:39
                    [status] => 0
                    [son] => Array
                        (
                            [6] => Array
                                (
                                    [id] => 6
                                    [name] => 修身
                                    [parent_id] => 5
                                    [sort] => 99
                                    [is_show] => 0
                                    [seller_id] => 0
                                    [part_img] => 
                                    [create_time] => 2018-06-27 15:20:39
                                    [update_time] => 2018-06-27 15:20:39
                                    [status] => 0
                                )

                            [7] => Array
                                (
                                    [id] => 7
                                    [name] => 正常
                                    [parent_id] => 5
                                    [sort] => 99
                                    [is_show] => 0
                                    [seller_id] => 0
                                    [part_img] => 
                                    [create_time] => 2018-06-27 15:20:39
                                    [update_time] => 2018-06-27 15:20:39
                                    [status] => 0
                                )

                            [8] => Array
                                (
                                    [id] => 8
                                    [name] => 宽松
                                    [parent_id] => 5
                                    [sort] => 99
                                    [is_show] => 0
                                    [seller_id] => 0
                                    [part_img] => 
                                    [create_time] => 2018-06-27 15:20:39
                                    [update_time] => 2018-06-27 15:20:39
                                    [status] => 0
                                )

                        )

                )

            [9] => Array
                (
                    [id] => 9
                    [name] => 领型宽
                    [parent_id] => 4
                    [sort] => 99
                    [is_show] => 0
                    [seller_id] => 0
                    [part_img] => 
                    [create_time] => 2018-06-27 15:20:39
                    [update_time] => 2018-06-27 15:20:39
                    [status] => 0
                    [son] => Array
                        (
                            [10] => Array
                                (
                                    [id] => 10
                                    [name] => 3CM
                                    [parent_id] => 9
                                    [sort] => 99
                                    [is_show] => 0
                                    [seller_id] => 0
                                    [part_img] => 
                                    [create_time] => 2018-06-27 15:20:39
                                    [update_time] => 2018-06-27 15:20:39
                                    [status] => 0
                                )

                            [11] => Array
                                (
                                    [id] => 11
                                    [name] => 4CM
                                    [parent_id] => 9
                                    [sort] => 99
                                    [is_show] => 0
                                    [seller_id] => 0
                                    [part_img] => 
                                    [create_time] => 2018-06-27 15:20:39
                                    [update_time] => 2018-06-27 15:20:39
                                    [status] => 0
                                )

                            [12] => Array
                                (
                                    [id] => 12
                                    [name] => 5CM
                                    [parent_id] => 9
                                    [sort] => 99
                                    [is_show] => 0
                                    [seller_id] => 0
                                    [part_img] => 
                                    [create_time] => 2018-06-27 15:20:39
                                    [update_time] => 2018-06-27 15:20:39
                                    [status] => 0
                                )

                            [13] => Array
                                (
                                    [id] => 13
                                    [name] => 5.5CM
                                    [parent_id] => 9
                                    [sort] => 99
                                    [is_show] => 0
                                    [seller_id] => 0
                                    [part_img] => 
                                    [create_time] => 2018-06-27 15:20:39
                                    [update_time] => 2018-06-27 15:20:39
                                    [status] => 0
                                )

                            [14] => Array
                                (
                                    [id] => 14
                                    [name] => 6CM
                                    [parent_id] => 9
                                    [sort] => 99
                                    [is_show] => 0
                                    [seller_id] => 0
                                    [part_img] => 
                                    [create_time] => 2018-06-27 15:20:39
                                    [update_time] => 2018-06-27 15:20:39
                                    [status] => 0
                                )

                            [15] => Array
                                (
                                    [id] => 15
                                    [name] => 6.5CM
                                    [parent_id] => 9
                                    [sort] => 99
                                    [is_show] => 0
                                    [seller_id] => 0
                                    [part_img] => 
                                    [create_time] => 2018-06-27 15:20:39
                                    [update_time] => 2018-06-27 15:20:39
                                    [status] => 0
                                )

                            [16] => Array
                                (
                                    [id] => 16
                                    [name] => 7CM
                                    [parent_id] => 9
                                    [sort] => 99
                                    [is_show] => 0
                                    [seller_id] => 0
                                    [part_img] => 
                                    [create_time] => 2018-06-27 15:20:39
                                    [update_time] => 2018-06-27 15:20:39
                                    [status] => 0
                                )

                            [17] => Array
                                (
                                    [id] => 17
                                    [name] => 8CM
                                    [parent_id] => 9
                                    [sort] => 99
                                    [is_show] => 0
                                    [seller_id] => 0
                                    [part_img] => 
                                    [create_time] => 2018-06-27 15:20:39
                                    [update_time] => 2018-06-27 15:20:39
                                    [status] => 0
                                )

                            [18] => Array
                                (
                                    [id] => 18
                                    [name] => 9CM
                                    [parent_id] => 9
                                    [sort] => 99
                                    [is_show] => 0
                                    [seller_id] => 0
                                    [part_img] => 
                                    [create_time] => 2018-06-27 15:20:39
                                    [update_time] => 2018-06-27 15:20:39
                                    [status] => 0
                                )

                        )

                )

        )

)

然后我去调用方法去统计这个数组

$this->getArrNum($arr);

    /**
     * 递归统计不规则数组的长度
     * @param $data
     * @param int $parent_id
     * @param int $level
     * @return array
     */
    public function getArrNum($data)
    {
        static $arr = 0;
        foreach ($data['son'] as $k => $v) {
            $arr++;
            if (array_key_exists('son', $v)) {
                $this->getArrNum($v);
            }
        }
        return $arr + 1;//因为之前的顶级数组没有统计好，所以需要加1
    }

然后就会显示统计的结果17了

ps:(如果哪位大牛又更好的办法。求指教)