Question

我有一个项目清单：

public class Item
{
    public int ItemId { get; set; }
    public string ItemName { get; set; }
    public int ListId { get; set; }
}

1 Test1 1

2 Test2 1

3 Test3 1

4 List 2

5 List2 2

6 Testing 3

7 Testing2 3

8 Testing3 3

我是否有办法按ListId分组并将它们放入每个单独的存储桶中，即ListId1存储桶将包含ListId == 1的所有项目。该列表是从SQL动态返回的，所以我事先不知道会有多少ListId。

Answer 1

您可以使用GroupBy：

var groups = items.GroupBy(item => item.ListId);

foreach(var group in groups)
{
     Console.WriteLine("List with ID == {0}", group.Key);
     foreach(var item in group)
        Console.WriteLine("    Item: {0}", item.ItemName);
}

Answer 2

让我们创建您的项目列表：

List<Item> items = new List<Item>();
items.Add(new Item() { ItemId = 1, ItemName = "Test1", ListId = 1 });
items.Add(new Item() { ItemId = 2, ItemName = "Test2", ListId = 1 });
items.Add(new Item() { ItemId = 3, ItemName = "Test3", ListId = 1 });
items.Add(new Item() { ItemId = 4, ItemName = "List", ListId = 2 });
items.Add(new Item() { ItemId = 5, ItemName = "List2", ListId = 2 });
items.Add(new Item() { ItemId = 6, ItemName = "Testing", ListId = 3 });
items.Add(new Item() { ItemId = 7, ItemName = "Testing2", ListId = 3 });
items.Add(new Item() { ItemId = 8, ItemName = "Testing3", ListId = 3 });

var groupByResult = items.GroupBy(i => i.ListId);

在此GroupBy调用之后，groupByResult是IEnumerable<IGrouping<int, Item>>类型的变量，它基本上是实现IGrouping接口的对象的集合。这允许您遍历所有项目，因为IGrouping派生自IEnumerable<>，并且有一个名为Key的额外字段：

public interface IGrouping<out TKey, out TElement> : IEnumerable<TElement>, IEnumerable
{
    TKey Key { get; }
}

简单地说，GroupBy方法调用会返回列表列表。外部列表对应于您在问题中提到的“桶”。然后每个“桶”包含与该“桶”对应的项目。为了特定于您的示例，groupByResult屏幕截图中显示了List<Item> firstBucketItems = groupByResult.First(i => i.Key == 1).ToList(); List<Item> secondBucketItems = groupByResult.First(i => i.Key == 2).ToList(); List<Item> thirdBucketItems = groupByResult.First(i => i.Key == 3).ToList();的值。我们可以看到，您的初始集合分为三个不同的桶，分别有3个，2个和3个项目。

至于访问这些组中的项目，您可以使用简单的LINQ：

foreach (var itemGroup in groupByResult)
{
    int groupKey = itemGroup.Key;

    foreach (Item item in itemGroup)
    {
        // Do whatever...
    }
}

First bucket items

或者您可以遍历所有项目：

CoreData

Answer 3

    IList<Student> studentList = new List<Student>()
    { 
    new Student() { StudentID = 1, StudentName = "John", Age = 18 } ,
    new Student() { StudentID = 2, StudentName = "Steve",  Age = 21 } ,
    new Student() { StudentID = 3, StudentName = "Bill",  Age = 18 } ,
    new Student() { StudentID = 4, StudentName = "Ram" , Age = 20 } ,
    new Student() { StudentID = 5, StudentName = "Abram" , Age = 21 } 
    };

var groupedResult = from s in studentList group s by s.Age;

//迭代每个小组

foreach (var ageGroup in groupedResult)
{
    Console.WriteLine("Age Group: {0}", ageGroup.Key); //Each group has a key 

    foreach(Student s in ageGroup) // Each group has inner collection
        Console.WriteLine("Student Name: {0}", s.StudentName);
}

Answer 4

基本格式

  var res = (from i in items
                           group i by i.ListId into g
                           select  );

Answer 5

您也可以按照以下步骤进行操作

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

public class Program
{
    public static void Main()
    {
        List<Item> items = new List<Item>();
        items.Add(new Item() { ItemId = 1, ItemName = "Test1", ListId = 1 });
        items.Add(new Item() { ItemId = 2, ItemName = "Test2", ListId = 1 });
        items.Add(new Item() { ItemId = 3, ItemName = "Test3", ListId = 1 });
        items.Add(new Item() { ItemId = 4, ItemName = "List", ListId = 2 });
        items.Add(new Item() { ItemId = 5, ItemName = "List2", ListId = 2 });
        items.Add(new Item() { ItemId = 6, ItemName = "Testing", ListId = 3 });
        items.Add(new Item() { ItemId = 7, ItemName = "Testing2", ListId = 3 });
        items.Add(new Item() { ItemId = 8, ItemName = "Testing3", ListId = 3 });

        var groupByResult = items.GroupBy(i => i.ListId);
        List<GroupedItems> betterGroups = new List<GroupedItems>();
        foreach (var groupedItem in groupByResult)
        {
            betterGroups.Add(new GroupedItems() { ListId = groupedItem.Key, Items = groupedItem.ToList() });
            // ListId = 1 , List<Item> 3 records 
            // ListId = 2 , List<Item> 2 records
            // ListId = 3 , List<Item> 3 records
            // You can iteratre throught ListId
        }
    }
    
    public class Item
    {
        public int ItemId { get; set; }
        public string ItemName { get; set; }
        public int ListId { get; set; }
    }
    
    public class GroupedItems
    {
        public int ListId {get; set;}
        public List<Item> Items {get; set;}
    }
}

donetFiddle示例Link

LINQ - GroupBy键，然后将每个分组项放入单独的“桶”中

5 个答案: