如何将自定义比较器与Linq Distinct方法一起使用?

问题描述

我正在读一本有关Linq的书，发现Distinct方法有一个需要比较器的重载.这将是一个解决我遇到的问题的好方法，我想从集合中获取不同的实体，但是即使其他属性不同，也希望对实体ID进行比较.

I was reading a book about Linq, and saw that the Distinct method has an overload that takes a comparer. This would be a good solution to a problem I have where I want to get the distinct entities from a collection, but want the comparison to be on the entity ID, even if the other properties are different.

根据这本书，如果我有一个Gribulator实体，我应该能够创建一个像这样的比较器...

According to the book, if I have a Gribulator entity, I should be able to create a comparer like this...

private class GribulatorComparer : IComparer<Gribulator> {
  public int Compare(Gribulator g1, Gribulator g2) {
    return g1.ID.CompareTo(g2.ID);
  }
}

...然后像这样使用它...

...and then use it like this...

List<Gribulator> distinctGribulators
  = myGribulators.Distinct(new GribulatorComparer()).ToList();

但是，这会导致以下编译器错误...

However, this gives the following compiler errors...

'System.Collections.Generic.List'不包含'Distinct'的定义，最佳扩展方法重载'System.Linq.Enumerable.Distinct(System.Collections.Generic.IEnumerable，System.Collections.Generic. IEqualityComparer)'有一些无效的参数

'System.Collections.Generic.List' does not contain a definition for 'Distinct' and the best extension method overload 'System.Linq.Enumerable.Distinct(System.Collections.Generic.IEnumerable, System.Collections.Generic.IEqualityComparer)' has some invalid arguments

参数2:无法从"LinqPlayground.Program.GribulatorComparer"转换为"System.Collections.Generic.IEqualityComparer"

Argument 2: cannot convert from 'LinqPlayground.Program.GribulatorComparer' to 'System.Collections.Generic.IEqualityComparer'

我进行了一些搜索，看到了很多使用此类代码的示例，但没有抱怨编译器错误.

I've searched around a bit, and have seen plenty of examples that use code like this, but no complaints about compiler errors.

我做错了什么?另外，这是最好的方法吗?我在这里想要一个一次性的解决方案，所以不想开始更改实体本身的代码.我希望该实体保持正常状态，但仅在这一位置，仅按ID比较即可.

What am I doing wrong? Also, is this the best way of doing this? I want a one-off solution here, so don't want to start changing the code for the entity itself. I want the entity to remain as normal, but just in this one place, compare by ID only.

感谢您的帮助.

推荐答案

您正在将比较器实现为IComparer<T>，LINQ方法重载需要实现IEqualityComparer:

You're implementing your comparer as an IComparer<T>, the LINQ method overload requires an implementation of IEqualityComparer:

private class GribulatorComparer : IEqualityComparer<Gribulator> {
  public bool Equals(Gribulator g1, Gribulator g2) {
    return g1.ID == g2.ID;
  }
}

为澄清起见，IComparer接口可用于排序，因为这基本上是Compare()方法的作用.

For clarification, the IComparer interface can be used for sorting, as that's basically what the Compare() method does.

赞:

items.OrderBy(x => new ItemComparer());

private class ItemComparer : IComparer<Item>
{
    public int Compare(Item x, Item y)
    {
        return x.Id.CompareTo(y.Id)
    }
}

哪个将使用该比较器对集合进行排序，但是LINQ提供了一种对简单字段(例如int Id)执行此操作的方法.

Which will sort your collection using that comparer, however LINQ provides a way to do that for simple fields (like an int Id).

items.OrderBy(x => x.Id);

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