将嵌套键值对分组到字典中

Question

我有以下代码：

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;


public class Test
{
    static void Main()
    {

        var list = new List<KeyValuePair<int, KeyValuePair<int, User>>>
                        {
                            new KeyValuePair<int, KeyValuePair<int, User>>(1,new KeyValuePair<int, User>(1,new User {FirstName = "Name1"})),
                            new KeyValuePair<int, KeyValuePair<int, User>>(1,new KeyValuePair<int, User>(1,new User {FirstName = "Name2"})),
                            new KeyValuePair<int, KeyValuePair<int, User>>(1,new KeyValuePair<int, User>(2,new User {FirstName = "Name3"})),
                            new KeyValuePair<int, KeyValuePair<int, User>>(1,new KeyValuePair<int, User>(2,new User {FirstName = "Name4"})),
                            new KeyValuePair<int, KeyValuePair<int, User>>(2,new KeyValuePair<int, User>(3,new User {FirstName = "Name5"})),
                            new KeyValuePair<int, KeyValuePair<int, User>>(2,new KeyValuePair<int, User>(3,new User {FirstName = "Name6"})),
                            new KeyValuePair<int, KeyValuePair<int, User>>(2,new KeyValuePair<int, User>(3,new User {FirstName = "Name6"})),
                            new KeyValuePair<int, KeyValuePair<int, User>>(3,new KeyValuePair<int, User>(4,new User {FirstName = "Name7"})),
                        };
    }
}
public class User
{
    public string FirstName { get; set; }
}

上面您可以看到第一个键值对的相同键有多个值，并且进一步（在第二个嵌套键值对中）有多个相同的键现在我想对它们进行分组并将列表对象转换为字典其中键将相同（如上所示的 1,2），但第一个值将是字典，第二个值将是集合。像这样：

var outputNeeded = new Dictionary<int,Dictionary<int,Collection<User>>>();

我该怎么做。 ??

Answer 1

您可以使用 LINQ：

var result = list
    .GroupBy(
        x => x.Key,
        x => x.Value)
    .ToDictionary(
        g => g.Key,
        g => g.GroupBy(
                  y => y.Key,
                  y => y.Value)
              .ToDictionary(
                  h => h.Key,
                  h => new Collection<User>(h.ToList())));

这会创建以下层次结构：

1
 \_ 1
 |   \_ Name1
 |   \_ Name2
 \_ 2
     \_ Name3
     \_ Name4
2
 \_ 3
     \_ Name5
     \_ Name6
     \_ Name6
3
 \_ 4
     \_ Name7

---

不过，嵌套字典通常不太好用。
我可能更喜欢一个简单的查找表：

var result = list
    .ToLookup(
        x => Tuple.Create(x.Key, x.Value.Key),
        x => x.Value.Value);