嵌套的ng-repeat双层循环，内层如何获取外层的$index?

html代码：

<div>
  <ul ng-repeat="row in table track by $index">
       <li ng-repeat="col in row track by col.id">
           <span ng-click="add(col, $index)">{{col.value}}</span>
       </li>
  </ul>
</div>

此时$index是内层循环的$index,那么如何获取外层的$index呢？有两种方法：

1、$parent.$index

2、用ng-init将外层循环进行保存

<div>
  <ul ng-repeat="row in table track by $index" ng-init="outerIndex=$index">
       <li ng-repeat="col in row track by col.id">
           <span ng-click="add(col, outerIndex)">{{col.value}}</span>
       </li>
  </ul>
</div>