检查对象列表C#中的重复项 [英] Checking for duplicates in a List of Objects C#

问题描述

我正在寻找一种非常快速的方法来检查对象列表中的重复项.

I am looking for a really fast way to check for duplicates in a list of objects.

我本来只是想简单地遍历列表并以这种方式进行手动比较，但是我认为linq可能会提供一个更优雅的解决方案...

I was thinking of simply looping through the list and doing a manual comparison that way, but I thought that linq might provide a more elegant solution...

假设我有一个对象...

Suppose I have an object...

public class dupeCheckee
{
     public string checkThis { get; set; }
     public string checkThat { get; set; }

     dupeCheckee(string val, string val2)
     {
         checkThis = val;
         checkThat = val2;
     }
}

我有这些对象的列表

List<dupeCheckee> dupList = new List<dupeCheckee>();
dupList.Add(new dupeCheckee("test1", "value1"));
dupList.Add(new dupeCheckee("test2", "value1"));
dupList.Add(new dupeCheckee("test3", "value1"));
dupList.Add(new dupeCheckee("test1", "value1"));//dupe
dupList.Add(new dupeCheckee("test2", "value1"));//dupe... 
dupList.Add(new dupeCheckee("test4", "value1"));
dupList.Add(new dupeCheckee("test5", "value1"));
dupList.Add(new dupeCheckee("test1", "value2"));//not dupe

我需要在该列表中找到骗子.当我找到它时，我需要做一些附加的逻辑 不一定要删除它们.

I need to find the dupes in that list. When I find it, I need to do some additional logic not necessarily removing them.

当我使用linq时，我的GroupBy如何引发异常...

When I use linq some how my GroupBy is throwing an exception...

'System.Collections.Generic.List<dupeCheckee>' does not contain a definition for 'GroupBy' and no extension method 'GroupBy' accepting a first argument of type 'System.Collections.Generic.List<dupeCheckee>' could be found (are you missing a using directive or an assembly reference?)

告诉我我缺少图书馆.我很难弄清楚哪一个.

Which is telling me that I am missing a library. I am having a hard time figuring out which one though.

一旦我弄清楚了，我基本上将如何检查这两个条件... IE的checkThis和checkThat都发生不止一次?

Once I figure that out though, How would I essentially check for those two conditions... IE checkThis and checkThat both occur more than once?

更新:我想出了什么

这是经过快速研究后想到的linq查询...

This is the linq query that I came up with after doing quick research...

test.Count != test.Select(c => new { c.checkThat, c.checkThis }).Distinct().Count()

我不确定这是否绝对比这个答案要好...

I am not certain if this is definitely better than this answer...

var duplicates = test.GroupBy(x => new {x.checkThis, x.checkThat})
                   .Where(x => x.Skip(1).Any());

我知道我可以将第一条语句放入if else子句中.我还进行了快速测试.重复列表在我期望为0时给了我1，但它确实正确地说明了我在其中一组使用的重复项中有重复的事实.

I know I can put the first statement into an if else clause. I also ran a quick test. The duplicates list gives me back 1 when I was expecting 0 but it did correctly call the fact that I had duplicates in one of the sets that I used...

另一种方法完全符合我的预期.这是我用来测试的数据集....

The other methodology does exactly as I expect it to. Here are the data sets that I use to test this out....

重复:

List<DupeCheckee> test = new List<DupeCheckee>{ 
     new DupeCheckee("test0", "test1"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test1", "test2"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test2", "test3"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test3", "test3"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test0", "test5"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test1", "test6"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test2", "test7"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test3", "test8"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test0", "test5"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test1", "test1"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test2", "test2"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test3", "test3"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test4", "test4"),//{ checkThis = "test", checkThat = "test1"}

};

没有欺骗...

     List<DupeCheckee> test2 = new List<DupeCheckee>{ 
     new DupeCheckee("test0", "test1"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test1", "test2"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test2", "test3"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test3", "test3"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test4", "test5"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test5", "test6"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test6", "test7"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test7", "test8"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test8", "test5"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test9", "test1"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test2", "test2"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test3", "test3"),//{ checkThis = "test", checkThat = "test1"}
     new DupeCheckee("test4", "test4"),//{ checkThis = "test", checkThat = "test1"}

};

推荐答案

您需要引用System.Linq(例如using System.Linq)

You need to reference System.Linq (e.g. using System.Linq)

那你就可以做

var dupes = dupList.GroupBy(x => new {x.checkThis, x.checkThat})
                   .Where(x => x.Skip(1).Any());

这将为您提供所有重复的组

This will give you groups with all the duplicates

然后将进行重复测试

var hasDupes = dupList.GroupBy(x => new {x.checkThis, x.checkThat})
                   .Where(x => x.Skip(1).Any()).Any();

或者甚至调用ToList()或ToArray()来强制计算结果，然后可以检查重复项并进行检查.

or even call ToList() or ToArray() to force the calculation of the result and then you can both check for dupes and examine them.

例如.

var dupes = dupList.GroupBy(x => new {x.checkThis, x.checkThat})
                   .Where(x => x.Skip(1).Any()).ToArray();
if (dupes.Any()) {
  foreach (var dupeList in dupes) {
    Console.WriteLine(string.Format("checkThis={0},checkThat={1} has {2} duplicates",
                      duplist.Key.checkThis, 
                      duplist.Key.checkThat,
                      duplist.Count() - 1));
  }

}

或者

var dupes = dupList.Select((x, i) => new { index = i, value = x})
                   .GroupBy(x => new {x.value.checkThis, x.value.checkThat})
                   .Where(x => x.Skip(1).Any());

为您提供分组，每组中的每个项目将原始索引存储在属性index中，并将项目存储在属性value

Which give you the groups which each item per group stores the original index in a property index and the item in the property value

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