c#交叉连接两个相同类型的列表

Question

所以这里我有一些代码，可以正常工作。但是我想将 select 部分更改为其他内容，我不确定我可以使用哪些其他方法来提供帮助。

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

public class Program
{
    public static void Main()
    {
        var all = new List<People>{new People{Id = 1, Name = "andy1", Age = null}, new People{Id = 2, Name = "andy2", Age = null}, new People{Id = 3, Name = "andy3", Age = null}, new People{Id = 4, Name = "andy4", Age = null}, };
        var someOfThem = new List<People>{new People{Id = 1, Name = null, Age = 1}, new People{Id = 2, Name = null, Age = 1},new People{Id = 3, Name = null, Age = 1}};
        var test = someOfThem.Select(c =>
        {
            c.Name = all.Find(a => a.Id == c.Id).Name;
            return c;
        });
        foreach (var item in test)
            Console.WriteLine("{0}={1}={2}", item.Id, item.Name, item.Age);
    }
}

public class People
{
    public int Id
    {
        get;
        set;
    }

    public int? Age
    {
        get;
        set;
    }


    public string Name
    {
        get;
        set;
    }
}

这是结果。

1=andy1=1
2=andy2=1
3=andy3=1

我只是想知道是否有另一种方法可以达到相同的结果但更优雅？或者更简单的方法？

        var test = someOfThem.Select(c =>
        {
            c.Name = all.Find(a => a.Id == c.Id).Name;
            return c;
        });

更新抱歉，我一开始没有正确显示我的问题，我已经更新了我的问题。请再看看。

Answer 1

您可以使用 C# 的 LINQ 关键字，更具体地说，是与之关联的 join 关键字：

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

public class Program
{
    public static void Main()
    {
        var all = new List<People> { new People { Id = 1, Name = "andy1", }, new People { Id = 2, Name = "andy2", }, new People { Id = 3, Name = "andy3", }, new People { Id = 4, Name = "andy4", }, };
        var someOfThem = new List<People> { new People { Id = 1, Name = null, }, new People { Id = 2, Name = null, } };
        var test = from item in someOfThem
                   join element in all on item.Id equals element.Id
                   select element;

        foreach (var item in test)
            Console.WriteLine("{0}={1}", item.Id, item.Name);
    }
}

public class People
{
    public int Id
    {
        get;
        set;
    }

    public string Name
    {
        get;
        set;
    }
}

代码版本为

var test = someOfThem.Join(all, item => item.Id, element => element.Id, (item, element) => element);

如罗伯特的评论所示

Answer 2

您可以在您的人脉 class 中实施 Equals 和 GetHashCode 并使用 Intersect。

或者，创建一个 EqualityComparer，这样你的比较逻辑就解耦了：

class Program
{

    public static void Main()
    {
        var all = new List<People> { new People { Id = 1, Name = "andy1", }, new People { Id = 2, Name = "andy2", }, new People { Id = 3, Name = "andy3", }, new People { Id = 4, Name = "andy4", }, };
        var someOfThem = new List<People> { new People { Id = 1, Name = null, }, new People { Id = 2, Name = null, } };

        var test = all.Intersect(someOfThem, new PeopleIdComparer()).ToList();

        foreach (var item in test)
            Console.WriteLine("{0}={1}", item.Id, item.Name);
    }
}

public class PeopleIdComparer : IEqualityComparer<People>
{
    public bool Equals(People x, People y)
    {
        return x.Id == y.Id;
    }

    public int GetHashCode(People obj)
    {
        return HashCode.Combine(obj.Id);
    }
}

public class People
{
    public int Id
    {
        get;
        set;
    }

    public string Name
    {
        get;
        set;
    }
}

Answer 3

你可以使用Join（你也可以使用字典，但我不会展示）：

这是连接的语法：

var test = someOfThem.Join(all, item => item.Id, element => element.Id, 
  (item, element) => new Person { 
    Id = item.Id ?? element.Id,
    Name = item.Name ?? element.Name,
    Age = item.Age ?? element.Age
  });

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