php计算二维数组中某一项之和的方法

数组示例：

[0] => array(3) {
   ["id"] => string(1 "1"
   ["name"] => string(4) "jhon"
   ["amount"] => string(3) "850"
  }
[1] => array(3) {
   ["id"] => string(1) "2"
   ["name"] => string(5) "david"
   ["amount"] => string(4) "1200"
  }
[2] => array(3) {
   ["id"] => string(1) "3"
   ["name"] => string(4) "lucy"
   ["amount"] => string(3) "200"
  }

需求说明：计算数组中所有元素的amount项的和。

方法一：

$total = array_sum(array_map(function($val){return $val['amount'];}, $arr));

方法二：

$total = 0;
foreach($arr as $item){
    $total += (int) $item['amount'];
}