C# 从子组中选择重复项答案

【问题标题】：C# select duplicates from sub-groupC# 从子组中选择重复项
【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，stackoverflow.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。

标签： c# linq lambda

【解决方案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

【解决方案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

【讨论】：