C＃LINQ在列表中找到重复的 [英] C# LINQ find duplicates in List

问题描述

使用LINQ，从列表< int> 中，如何检索包含多次重复的条目的列表及其值？

Using LINQ, from a List<int>, how can I retrieve a list that contains entries repeated more than once and their values?

推荐答案

解决问题的最简单的方法是根据它们的值对元素进行分组，然后选择组中的代表，如果有多个元素在组中。在linq中，这意味着：

The easiest way to solve the problem is to group the elements based on their value, and then pick a representative of the group if there are more than one element in the group. In linq, this translates to:

var query = lst.GroupBy(x=>x)
              .Where(g=>g.Count()>1)
              .Select(y=>y.Key)
              .ToList();

如果您想知道重复元素的次数，可以使用：

If you want to know how many times the elements are repeated, you can use:

var query = lst.GroupBy(x=>x)
              .Where(g=>g.Count()>1)
              .Select(y=> new { Element = y.Key, Counter = y.Count()})
              .ToList();

这将返回一个匿名类型的列表，每个元素将具有属性Element和Counter，检索您需要的信息。

This will return a List of an anonymous type, and each element will have the properties Element and Counter, to retrieve the informations you need.

最后，如果它是您正在寻找的字典，可以使用

And lastly, if it's a dictionary you are looking for, you can use

var query = lst.GroupBy(x=>x)
              .Where(g=>g.Count()>1)
              .ToDictionary(x=>x.Key,y=>y.Count());

这将返回一个字典，其元素为关键字，重复次数为值。

This will return a dictionary, with your element as key, and the number of times it's repeated as value.

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