Distinct()如何工作? [英] How does Distinct() work?

问题描述

让我说这个:

class Foo
{
    public Guid id;
    public string description;
}

var list = new List<Foo>();
list.Add(new Foo() { id = Guid.Empty, description = "empty" });
list.Add(new Foo() { id = Guid.Empty, description = "empty" });
list.Add(new Foo() { id = Guid.NewGuid(), description = "notempty" });
list.Add(new Foo() { id = Guid.NewGuid(), description = "notempty2" });

现在，当我这样做时:

list = list.Distinct().Tolist();

它显然返回4个元素.我想要一个方法，该方法将比较我在类中拥有的所有数据，并返回唯一的元素，以检查类的每个属性.我需要编写自己的比较器，还是内置的东西可以这种方式工作?

It obviously returns 4 elements. I would like a method, that compares all the data i have in class, and returns unique elements, something that checks every property of the class. Do i need to write my own comparer, or is there something that is built-in that works this way?

推荐答案

您必须重写Foo.Equals(随后是Foo.GetHashCode)以显式比较每个字段.否则，它将使用默认实现Object.Equals(ReferenceEquals).

You have to override Foo.Equals (and subsequently Foo.GetHashCode) to explicitly compare each field. Otherwise it will use the default implementation, Object.Equals (ReferenceEquals).

或者，您可以将IEqualityComparer显式传递给Distinct()方法.

Or, you can explicitly pass an IEqualityComparer to the Distinct() method.

请注意，尽管使用匿名类确实会返回3个元素.根据您要使用Foo的位置以及所需的编译时类型安全性，可以执行以下操作:

Note though that using anonymous classes does return 3 elements. Depending on where you want to use Foo and how much compile-time type safety you need, you could do:

var list = new List<dynamic>();
list.Add(new { id = Guid.Empty, description = "empty" });
list.Add(new { id = Guid.Empty, description = "empty" });
list.Add(new { id = Guid.NewGuid(), description = "notempty" });
list.Add(new { id = Guid.NewGuid(), description = "notempty2" });

list = list.Distinct().ToList(); //3 elements selected

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