如何在codeigniter中初始化foreach循环中的整数数组

我在codeigniter项目的控制器中有以下代码:

foreach($attendace as $k => $v) { 
$id = $v['project_id'];
$result[$id]['project_name'] = $v['project_name']; 
$result[$id]['labour'] += $v['no_of_labours']; 
$result[$id]['total_time'] += ($v['stop_time']-$v['start_time'])*$v['no_of_labours']; 
}

此代码提供一个错误未知变量人工和总时间。如果我尝试初始化这些变量如下:

 foreach($attendace as $k => $v) { 
    $id = $v['project_id'];
    $result[$id]['labour'] =0;
    $result[$id]['total_time']=0;
    $result[$id]['project_name'] = $v['project_name']; 
    $result[$id]['labour'] += $v['no_of_labours']; 
    $result[$id]['total_time'] += ($v['stop_time']-$v['start_time'])*$v['no_of_labours']; 
    }

添加$result[$id]['labour']=0;和$result[$id]['total_time']=0;则我得到的附加值是错误的。基本上不会增加。

因此,谁能告诉我如何解决这个问题?