Question

假设我有一份期刊清单：

class Journal { public int ID; public string Name; }

var objListJournals = new List<Journal>
{
    new Journal{ID = 1, Name = "Tom"}, new Journal{ID = 2, Name = "Jerry"}, 
    new Journal{ID = 1, Name = "Brad"}, new Journal{ID = 3, Name = "Frog"}, 
    new Journal{ID = 1, Name = "Alex"}, new Journal{ID = 2, Name = "Don"}
};

现在我想要的是，这个列表将根据ID明智分割。所以它应该是这样的：

list 1: {ID=1, Name="Tom"},{ID=1, Name="Brad"}, {ID=1, Name="Alex"}
list 2: {ID=2, Name="Jerry"}, {ID=2, Name="Don"} 
list 3: {ID=3, Name="Frog"}

以便我可以将它们添加到新列表中 -

List<Journal> objNewList = new List<List<Journal>>();

objNewList.Add(list1);
objNewList.Add(list2);
..........

怎么办？

Answer 1

假设您的问题包含有效代码：

class Journal { public int ID; public string Name; }

var journals = new List<Journal>
{
    new Journal{ID = 1, Name = "Tom"}, new Journal{ID = 2, Name = "Jerry"}, 
    new Journal{ID = 1, Name = "Brad"}, new Journal{ID = 3, Name = "Frog"}, 
    new Journal{ID = 1, Name = "Alex"}, new Journal{ID = 2, Name = "Don"}
};

实际上编译为列表，您可以使用Linq groupby将实例中的一个成员分组到组中。

这会为您提供一个IEnumerable<IGrouping<int,Journal>>，您可以使用Select到IEnumerable<List<Journal>>来展平 - 如果您确实需要List<List<Journal>>，请致电ToList()在那：

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

public class Program
{
    class Journal { public int ID; public string Name; }

    static void T()
    {
        var journals = new List<Journal>
        {
            new Journal{ID = 1, Name = "Tom"}, new Journal{ID = 2, Name = "Jerry"}, 
            new Journal{ID = 1, Name = "Brad"}, new Journal{ID = 3, Name = "Frog"}, 
            new Journal{ID = 1, Name = "Alex"}, new Journal{ID = 2, Name = "Don"}};

        var listById = journals
            .GroupBy(j => j.ID)       // grouping into IEnumerable<IGrouping<int,Journal>>
            .Select(i => i.ToList()); // flattening to IEnumerable<List<Journal>

        foreach(var list in listById)
            Console.WriteLine(string.Join(",", 
                list.Select(l => string.Format("ID: {0} -  NAME: {1}", l.ID , l.Name))));
    }

    public static void Main()
    {
        T();
    }
}

输出：

ID: 1 -  NAME: Tom,ID: 1 -  NAME: Brad,ID: 1 -  NAME: Alex
ID: 2 -  NAME: Jerry,ID: 2 -  NAME: Don
ID: 3 -  NAME: Frog

Answer 2

在没有列表清单的情况下解决此问题的另一种方法：

            var journals = new List<Journal>
        {
            new Journal {ID = 1, Name = "Tom"},
            new Journal {ID = 2, Name = "Jerry"},
            new Journal {ID = 1, Name = "Brad"},
            new Journal {ID = 3, Name = "Frog"},
            new Journal {ID = 1, Name = "Alex"},
            new Journal {ID = 2, Name = "Don"}
        };
        var res =
            journals.GroupBy(x => x.ID, y => y.Name)
                .Select(x => new {ID = $"ID: {x.Key}" , Names = $"NAMES: {string.Join(", ", x)}"})
                .ToList();
        foreach (var item in res)
        {
            Console.WriteLine($"{item.ID} {item.Names}");
        }

Answer 3

您可以使用GroupBy;

var result = objJournalList.GroupBy(x => x.Id).Select(x => x.Select(k => k));

将列表拆分为子列表ID C＃

3 个答案: