Linq从另一个列表中获取列表 [英] Linq getting a list from another list

问题描述

我有两个集合:一个是Items，另一个是ActiveItems

I have two collections: one is Items And Another is ActiveItems

这两个集合之间唯一的交集是名称

The only intersection between these two collection is Name

我想要一个包含Linq的项目列表，其中项目名称位于具有该名称的ActiveItems中

I want a list with Linq from Items where the Items names are in the ActiveItems with that name

我写这段代码有一个更好的主意:

I wrote this code is there a better idea:

Items.Where(i => ActiveItems.Count(v=> v.Name==i.Name) > 0)

推荐答案

我可能会从ActiveItems创建一组名称，然后使用它:

I would probably create a set of the names from ActiveItems and then use that:

var activeNames = new HashSet<string>(activeItems.Select(x => x.Name));
var itemsWithActiveNames = items.Where(x => activeNames.Contains(x.Name))
                                .ToList();

另一种选择是使用联接，例如带有查询表达式:

Another option is to use a join, e.g. with a query expression:

var query = from activeItem in activeItems
            join item in items on activeItem.Name equals item.Name
            select item;

请注意，如果存在多个具有相同名称的ActiveItem值，这将给出重复的item值.另一个替代联接，它没有这个问题，但是有点笨拙:

Note that this will give duplicate item values if there are multiple ActiveItem values with the same name. Another alternative join, which doesn't have this problem but is a bit clumsier:

var query = from item in items
            join activeItem in activeItems 
                on item.Name equals activeItem.Name
                into g
            where g.Any()
            select item;

请注意，所有这些都将避免O(N * M)检查名称-它们都将在后台使用哈希表，从而带来O(N + M)的复杂性.

Note that all of these will avoid the O(N * M) check for names - they'll all use hash tables behind the scenes, to give an O(N + M) complexity.

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