使用特定比较规则的集合运算

发布于 2024-09-28 14:26:34 字数 359 浏览 0 评论 0原文

我有两个列表：

List<User> collection1 = new List<User>();
List<User> collection2 = new List<User>();

1) 我必须使用 LINQ 获取两个列表共有的所有项目。但是，User 类有很多属性，我只想比较 FirstName 和 LastName。

2) 如何使用相同的比较规则获取 collection1 中的项目而不是 collection2 中的项目？

原文

I have two lists:

List<User> collection1 = new List<User>();
List<User> collection2 = new List<User>();

1) I have to get all items common to both of the lists using LINQ. However, the class User has a lot of properties and I just want to compare FirstName and LastName.

2) How can I get the items in collection1 but not in collection2 using the same comparison rule?

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冷心人i 2024-10-05 14:26:34

对于第一个问题使用 Enumerable.Intersect第二个是Enumerable.Except。也就是说：

var common = collection1.Intersect(collection2, new UserEqualityComparer());
var difference = collection1.Except(collection2, new UserEqualityComparer());

当然，这里我假设 UserEqualityComparer 实现 IEqualityComparer 如下：

class UserEqualityComparer : IEqualityComparer<User> {
    public bool Equals(User x, User y) {
        if (Object.ReferenceEquals(x, y)) {
            return true;
        }
        if (x == null || y == null) {
            return false;
        }
        return x.FirstName == y.FirstName && x.LastName == y.LastName;
    }

    public int GetHashCode(User obj) {
        if (obj == null) {
            return 0;
        }
        return 23 * obj.FirstName.GetHashCode() + obj.LastName.GetHashCode();
    }
}

Use Enumerable.Intersect for the first question and Enumerable.Except for the second. To wit:

var common = collection1.Intersect(collection2, new UserEqualityComparer());
var difference = collection1.Except(collection2, new UserEqualityComparer());

Here, of course, I am assuming that UserEqualityComparer implements IEqualityComparer<User> like so:

class UserEqualityComparer : IEqualityComparer<User> {
    public bool Equals(User x, User y) {
        if (Object.ReferenceEquals(x, y)) {
            return true;
        }
        if (x == null || y == null) {
            return false;
        }
        return x.FirstName == y.FirstName && x.LastName == y.LastName;
    }

    public int GetHashCode(User obj) {
        if (obj == null) {
            return 0;
        }
        return 23 * obj.FirstName.GetHashCode() + obj.LastName.GetHashCode();
    }
}

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