如何在不使用$index的情况下计算嵌套ng-repeat中的项

$scope.items = [
    {
        name: 'Item 1',
        subItems: [
            { name: 'Sub Item 1' },
            { name: 'Sub Item 2' },
            { name: 'Sub Item 3' }
        ]
    },
    {
        name: 'Item 2',
        subItems: [
            { name: 'Sub Item 4' },
            { name: 'Sub Item 5' }
        ]
    },
    {
        name: 'Item 3',
        subItems: [
            { name: 'Sub Item 6' },
            { name: 'Sub Item 7' },
            { name: 'Sub Item 8' }
        ]
    }
];

<div ng-repeat="item in items">
    <h3>{{ item.name }}</h3>
    <div ng-repeat-start="subItem in item.subItems"></div>
    <p>{{ subItem.name }}</p>
    <div ng-repeat-end></div>
</div>

app.directive('nestedRepeat', function() {
    return {
        restrict: 'A',
        scope: {
            data: '=',
            calculate: '='
        },
        template: '<div ng-repeat="item in data">{{ calculate(item) }}</div>'
    };
});

<div nested-repeat data="items" calculate="calculateFunction"></div>

$scope.calculateFunction = function(item) {
    // 在这里进行计算，并返回结果
    // 可以根据item的属性进行不同的计算逻辑
};