C# 从子组中选择重复项

Posted 2023-03-31

【中文标题】C# 从子组中选择重复项

【英文标题】：C# select duplicates from sub-group

【发布时间】：2021-10-28 05:03:54

【问题描述】：

我想过滤掉 "" 名称，然后选择每个存在重复 ID 的唯一位置，而不考虑名称：

数据设置

var list = new[]

    new  id = 3, Name = "", Location = "LocationA" ,
    new  id = 2, Name = "", Location = "LocationA" ,
    new  id = 1, Name = "T", Location = "LocationB" ,
    new  id = 2, Name = "H", Location = "LocationB" ,
    new  id = 3, Name = "E", Location = "LocationB" ,
    new  id = 3, Name = "R", Location = "LocationB" ,
    new  id = 5, Name = "U", Location = "LocationC" ,
    new  id = 5, Name = "S", Location = "LocationC" ,
    new  id = 5, Name = "S", Location = "LocationD" ,
    new  id = 4, Name = "O", Location = "LocationD" ,
    new  id = 4, Name = "Z", Location = "LocationE" ,
;

查询

var query1 = list
    .Where(s => s.Name != "")
    .GroupBy(g => g.Location)
    .Where(w => w.Select(s => s.Location).Count() > 1)
    .SelectMany(s => s)
    .GroupBy(g => g.id)
    .Where(w => w.Select(s => s.id).Count() > 1)
    .SelectMany(s => s)
    .ToList();
Console.WriteLine("output\n" + string.Join("\n", query1));

退货

 id = 3, Name = E, Location = LocationB 
 id = 3, Name = R, Location = LocationB 
 id = 5, Name = U, Location = LocationC 
 id = 5, Name = S, Location = LocationC 
 id = 5, Name = S, Location = LocationD 

vs我真正想要的

 id = 3, Name = E, Location = LocationB 
 id = 3, Name = R, Location = LocationB 
 id = 5, Name = U, Location = LocationC 
 id = 5, Name = S, Location = LocationC 

LocationD 的 ID 为 4 和 5，因此它应该被过滤掉，但我无法这样做。我究竟做错了什么？如何更正？

【问题讨论】：

我猜你又在问类似的问题，***.com/q/69733137/6299857

这能回答你的问题吗？ C# select duplicate using group

不，不是，如果您使用该查询的输入运行该查询的解决方案，您将获得 7 个返回与 4 的实际答案。这里的查询不同，我希望先进行多个分组或分组然后再次重新组合，而不是之前对单个组的查询。

【参考方案1】：

给定

var list = new[]

   new  id = 3, Name = "", Location = "LocationA" ,
   new  id = 2, Name = "", Location = "LocationA" ,
   new  id = 1, Name = "T", Location = "LocationB" ,
   new  id = 2, Name = "H", Location = "LocationB" ,
   new  id = 3, Name = "E", Location = "LocationB" ,
   new  id = 3, Name = "R", Location = "LocationB" ,
   new  id = 5, Name = "U", Location = "LocationC" ,
   new  id = 5, Name = "S", Location = "LocationC" ,
   new  id = 5, Name = "S", Location = "LocationD" ,
   new  id = 4, Name = "O", Location = "LocationD" ,
   new  id = 4, Name = "Z", Location = "LocationE" ,
;

示例

var results = list
   .Where(s => s.Name != "")
   .GroupBy(x => new x.id, x.Location)
   .Where(g => g.Count() > 1)
   .SelectMany(y => y);

foreach (var result in results)
   Console.WriteLine($"result.id, result.Name, result.Location");

输出

3, E, LocationB
3, R, LocationB
5, U, LocationC
5, S, LocationC

【讨论】：

您好 TheGeneral，您昨天已经回答了同一个 OP 提出的相同问题。我不知道为什么 OP 会问类似的问题，而不是自己阅读并付出一些努力

@PrasadTelkikar 啊，是的。 ops 当前的尝试肯定是过头了

感谢 Gen 的帮助，我昨天在工作中尝试了以前的解决方案，然后意识到这不是我想要的，所以我再次完善了我的查询。您的解决方案在这里很完美，可以解决问题

【参考方案2】：

按id 和Location 分组。并且得到.Count()超过1个。

var query1 = list
    .Where(s => s.Name != "")
    .GroupBy(g => new  g.Location, g.id )
    .Where(g => g.Count() > 1)
    .SelectMany(g => g)
    .ToList();

Sample demo