我有一个列表集合，每个列表都有一个项目数组。我需要在每个列表上按id对项目进行分组。
当我尝试重新分配$list-〉items时，什么都没有发生，但是如果我重新分配$list-〉name，它就起作用了，所以问题是对象的数组或数组属性，或者类似的东西...
要重新指派集合内的数组，我必须执行什麽动作？

$lists = Listt::with('items')->get();
    $newLists = $lists->map(function(Listt $list) {

        // $list->items = $list->items->groupBy('id'); // this is what I want, it doesn't work
        // $list->items = []; // this doesn't work either
        // $list['items'] = []; // nope
        // $list->items = new Collection(); // nope
        $list->items = collect([... $list->items])->groupBy('id');// nope

        $list->name = 'test'; //this works, so the problem is arrays <----

        return $list;
    });
    return $newLists;

    /* transform doesn't work */
    // $lists->transform(function(Listt $list) {
        //... 
    // });
    // return $lists;

    /* this, from a similar question, doesn't work either, besides I don't understand it and it doesn't use collection methods... */
    // foreach($lists as &$list){
    //    $list['items'] = [];
    //    unset($list);
    // }
    // return $lists;