从列表中获取对象的数量？

Question

public class Agenda 
{

public string StartDate;

public string EndDate;

public string Id;

}

public Class Appointments

{

public Agenda agenda;

。

public class ViewModel

我

List<Appointments> collection = new List<Appointments>();    

collection.Add(new Agenda { StartDate = "date1" , EndDate = "date1", Id= "1234567" } );

collection.Add(new Agenda { StartDate = "date2" , EndDate = "date2", Id= "1234567" } );

collection.Add(new Agenda { StartDate = "date3" , EndDate = "date3", Id= "2222222" } );

collection.Add(new Agenda { StartDate = "date4" , EndDate = "date4", Id= "3333333" } );

collection.Add(new Agenda { StartDate = "date5" , EndDate = "date5", Id= "3333333" } );

collection.Add(new Agenda { StartDate = "date1" , EndDate = "date1", Id= "3333333" } );

collection.Add(new Agenda { StartDate = "date1" , EndDate = "date1", Id= "1234567" } );

}

希望 Linq 解决方案从 Viewmodel *Appointement* 属性获取 议程 的数量，

例如 Id = "1234567" 列表中有 3 个议程对象

Id = "3333333" has 3 Agenda object in List

Id = "2222222" has 2 Agenda object in List












enter code here

Answer 1

var groups = collection.GroupBy(x => x.Id);
foreach(var group in groups) {
    Console.WriteLine("Count for Id {0}: {1}", group.Key, group.Count());
}

Answer 2

（从 ViewModel.collection 中的 a.Id.Equals("1234567") 选择 a).Count();