C#中两个列表的联接 [英] join of two lists in c#

问题描述

public class Co
{
    public int Id { get; set; }
    public string Title { get; set; }
    public List<string> Cards { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        List<Co> coll = new List<Co>();
        Co c1 = new Co();
        c1.Id = 1;
        c1.Title = "A";
        coll.Add(c1);
        Co c2 = new Co();
        c2.Id = 2;
        c2.Title = "B";
        coll.Add(c2);
        List<KeyValuePair<int, int>> list = new List<KeyValuePair<int, int>>();
        list.Add(new KeyValuePair<int, int>(1, 2));
        list.Add(new KeyValuePair<int, int>(1, 3));
        list.Add(new KeyValuePair<int, int>(1, 1));
        list.Add(new KeyValuePair<int, int>(2, 1));

        Console.ReadKey();
    }

我想通过比较coll中对象的id和list

I want to assign Cards property for all the objects in coll with comma separated values of value in list by comparing the id from object in coll with key from list

输出:对于第一个对象c.Cards ="2,3,1" 对于第二个对象c.cards =" 1"

Output: for first object c.Cards ="2,3,1" for second object c.cards= "1"

我可以通过foreach循环来做到这一点.谁能告诉我使用linq的解决方案?

I'm able to do it with foreach loops. Can anyone tell me the solution with linq?

推荐答案

首先，请注意您的示例数据不正确，因为您两次使用同一c对象.应该是这样的:

First, note that your sample data is incorrect because you use the same c object twice. It should be like:

List<Co> coll = new List<Co>();
Co c = new Co();
c.Id = 1;
c.Title = "A";
coll.Add(c);
c = new Co(); // HERE
c.Id = 2;
c.Title = "B";
coll.Add(c);
List<KeyValuePair<int, int>> list = new List<KeyValuePair<int, int>>();
list.Add(new KeyValuePair<int, int>(1, 2));
list.Add(new KeyValuePair<int, int>(1, 3));
list.Add(new KeyValuePair<int, int>(1, 1));
list.Add(new KeyValuePair<int, int>(2, 1));

现在，请注意，您的Cards属性是List<string>，而不是string，因此我不知道逗号分隔值"的含义.如果Cards是字符串:

Now, note that your Cards property is a List<string>, not a string, so I don't know what you mean by "comma separated values". If Cards were a string:

coll.ForEach(co => co.Cards = String.Join(",",
    list.Where(l => l.Key == co.Id)
        .Select(l => l.Value)));

您当前的定义为List<string>:

coll.ForEach(co => co.Cards =
    list.Where(l => l.Key == co.Id)
        .Select(l => l.Value.ToString()).ToList()
);

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