Question

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。

我在考虑简单地循环遍历列表并以这种方式进行手动比较，但我认为linq可能会提供更优雅的解决方案......

假设我有一个对象......

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

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

我有一个这些对象的列表

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

我需要找到该列表中的欺骗行为。当我找到它时，我需要做一些额外的逻辑不一定要删除它们。

当我使用linq时，我的GroupBy如何抛出异常......

'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?)

这告诉我，我错过了一个图书馆。我很难搞清楚哪一个。

一旦我弄明白了，我将如何检查这两个条件...... IE checkThis和checkThat都发生了不止一次？

更新：我想出了什么

这是我在快速研究后想出的linq查询...

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

我不确定这肯定比这个答案更好......

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个语句放入if else子句中。我也进行了快速测试。当我期待0时，重复列表给了我1但它确实正确地称我在我使用的其中一个集合中有重复的事实......

另一种方法完全按照我的预期进行。以下是我用来测试它的数据集....

愚弄：

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"}

};

Answer 1

您需要引用System.Linq（例如using System.Linq）

然后你可以做

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

这将为您提供包含所有重复项的组

重复的测试将是

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

甚至致电ToList()或ToArray()以强制计算结果，然后您可以检查欺骗并检查它们。

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));
  }

}

可选地

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());

为您提供每组中每个项目将原始索引存储在属性index中以及属性value

中的项目的组

Answer 2

有大量的工作解决方案，但我认为下一个解决方案将更加透明和易于理解，然后以上所有：

var hasDuplicatedEntries = ListWithPossibleDuplicates
                                   .GroupBy(YourGroupingExpression)
                                   .Any(e => e.Count() > 1);
if(hasDuplicatedEntries)
{
   // Do what ever you want in case when list contains duplicates 
}

Answer 3

我认为这就是你要找的东西：

List<dupeChecke> duplicates = dupeList.GroupBy(x => x)
                                   .SelectMany(g => g.Skip(1));

Answer 4

选择与linq不同的选项，例如： How can I do SELECT UNIQUE with LINQ?

然后将不同结果的计数与非不同结果进行比较。如果列表有双打，那将给你一个布尔说法。

此外，您可以尝试使用字典，这将保证密钥是唯一的。

Answer 5

对于内存对象，我总是使用Distinct LINQ方法为解决方案添加一个比较器。

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

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

     public class Comparer : IEqualityComparer<dupeCheckee>
     {
         public bool Equals(dupeCheckee x, dupeCheckee y)
         {
             if (x == null || y == null)
                 return false;

             return x.CheckThis == y.CheckThis && x.CheckThat == y.CheckThat;
         }

         public int GetHashCode(dupeCheckee obj)
         {
             if (obj == null)
                 return 0;

             return (obj.CheckThis == null ? 0 : obj.CheckThis.GetHashCode()) ^
                 (obj.CheckThat == null ? 0 : obj.CheckThat.GetHashCode());
         }
     }
}

现在我们可以致电

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

var distinct = dupList.Distinct(dupeCheckee.Comparer);

Answer 6

我喜欢用它来知道什么时候有任何重复。让我们说你有一个字符串，想知道是否有任何重复的字母。这就是我使用的。

string text = "this is some text";

var hasDupes = text.GroupBy(x => x).Any(grp => grp.Count() > 1);

如果您想知道有多少重复项，无论重复项是什么，请使用此项。

var totalDupeItems = text.GroupBy(x => x).Count(grp =>  grp.Count() > 1);

例如，＆＃34;这是一些文字＆＃34;有这个...

总共字母t：3

总信件i：2

总共字母s：3

总共字母e：2

因此变量totalDupeItems等于4.有4种不同的重复项。

如果您想获得欺骗物品的总量，无论这些物品是什么，请使用此物品。

var totalDupes = letters.GroupBy(x => x).Where(grp => grp.Count() > 1).Sum(grp => grp.Count());

因此变量totalDupes将为10.这是每个重叠类型的重复项总数。

检查对象列表C＃中的重复项

6 个答案: