Question

例如，我有列表

Rating rate1 = new Rating { artistID = 1, userID = 101, rating = 2 };
Rating rate2 = new Rating { artistID = 1, userID = 102, rating = 4 };
Rating rate3 = new Rating { artistID = 2, userID = 101, rating = 3 };
Rating rate4 = new Rating { artistID = 2, userID = 102, rating = 5 };
Rating rate5 = new Rating { artistID = 2, userID = 103, rating = 1 };
Rating rate6 = new Rating { artistID = 3, userID = 102, rating = 1 };
Rating rate7 = new Rating { artistID = 3, userID = 103, rating = 1 };

List<Rating> ratings = new List<Rating>(7);
ratings.Add(rate1);
ratings.Add(rate2);
ratings.Add(rate3);
ratings.Add(rate4);
ratings.Add(rate5);
ratings.Add(rate6);
ratings.Add(rate7);

我有第二个清单，

List<Rating> ratings2 = new List<Rating>(2);
ratings2.Add(rate1);
ratings2.Add(rate3);

现在我要使用List<Rating> ratings过滤List<Rating> ratings2。

在此cace中，我们使用artistID元素来过滤评分列表，换句话说，我想要包含列出artistID 1 AND 2 的所有列表在评级2

谢谢。

Answer 1

如果您只想比较artistID，那么您可以这样做：

List<Rating> resultList = ratings.Where(r => ratings2.Select(t => t.artistID)
                                             .Contains(r.artistID))
                                             .ToList();

以上将选择artistIDs作为第二个列表ratings2进行类似于SELECT * from Table WHERE ID IN (1,2)的比较

Answer 2

您可以使用HashSet<int>作为快速查找：

var r2Artists = new HashSet<int>(ratings2.Select(r2 => r2.artistID));
var result = ratings.Where(r => r2Artists.Contains(r.artistID));

如何按列表元素过滤列表

2 个答案: