如何通过 Lambda 或 LINQ 从列表中获取不同的实例 [英] How to get distinct instance from a list by Lambda or LINQ

问题描述

我有一堂这样的课:

class MyClass<T> {
    public string value1 { get; set; }
    public T objT { get; set; }
}

和这个类的列表.我想使用 .net 3.5 lambda 或 linq 通过不同的 value1 获取 MyClass 列表.我想这是可能的，而且比 .net 2.0 中缓存这样的列表的方法简单得多:

and a list of this class. I would like to use .net 3.5 lambda or linq to get a list of MyClass by distinct value1. I guess this is possible and much simpler than the way in .net 2.0 to cache a list like this:

List<MyClass<T>> list; 
...
List<MyClass<T>> listDistinct = new List<MyClass<T>>();
foreach (MyClass<T> instance in list)
{
    // some code to check if listDistinct does contain obj with intance.Value1
    // then listDistinct.Add(instance);
}

使用 lambda 或 LINQ 的方法是什么?

What is the lambda or LINQ way to do it?

推荐答案

Marc 和 dahlbyk 的答案似乎都非常有效.不过，我有一个更简单的解决方案.您可以使用 GroupBy 而不是使用 Distinct.它是这样的:

Both Marc's and dahlbyk's answers seems to work very well. I have a much simpler solution though. Instead of using Distinct, you can use GroupBy. It goes like this:

var listDistinct
    = list.GroupBy(
        i => i.value1,
        (key, group) => group.First()
    ).ToArray();

请注意，我已将两个函数传递给 GroupBy().第一个是键选择器.第二个从每组中只得到一个项目.根据您的问题，我认为 First() 是正确的.如果你愿意，你可以写一个不同的.你可以试试 Last() 看看我的意思.

Notice that I've passed two functions to the GroupBy(). The first is a key selector. The second gets only one item from each group. From your question, I assumed First() was the right one. You can write a different one, if you want to. You can try Last() to see what I mean.

我使用以下输入进行了测试:

I ran a test with the following input:

var list = new [] {
    new { value1 = "ABC", objT = 0 },
    new { value1 = "ABC", objT = 1 },
    new { value1 = "123", objT = 2 },
    new { value1 = "123", objT = 3 },
    new { value1 = "FOO", objT = 4 },
    new { value1 = "BAR", objT = 5 },
    new { value1 = "BAR", objT = 6 },
    new { value1 = "BAR", objT = 7 },
    new { value1 = "UGH", objT = 8 },
};

结果是:

//{ value1 = ABC, objT = 0 }
//{ value1 = 123, objT = 2 }
//{ value1 = FOO, objT = 4 }
//{ value1 = BAR, objT = 5 }
//{ value1 = UGH, objT = 8 }

我还没有测试它的性能.我相信这个解决方案可能比使用 Distinct 的解决方案慢一点.尽管有这个缺点，但有两个很大的优点:简单性和灵活性.通常，更倾向于简单而不是优化，但这实际上取决于您要解决的问题.

I haven't tested it for performance. I believe that this solution is probably a little bit slower than one that uses Distinct. Despite this disadvantage, there are two great advantages: simplicity and flexibility. Usually, it better to favor simplicity over optimization, but it really depends on the problem you're trying to solve.

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