Question

public class Event
{
    public int Id { get; set; }
    public string Emp { get; set; }
    public DateTime EventDate { get; set; }
    public DateTime AccessTime { get; set; }
}

var events = new List<Event>(){
    new Event(){Id=1,Emp ="A",EventDate= new DateTime(2017, 1, 2), AccessTime= DateTime.Now},
    new Event(){Id=2,Emp ="A",EventDate= new DateTime(2017, 1, 2), AccessTime= DateTime.Now.AddMinutes(4)},
    new Event(){Id=3,Emp ="A",EventDate= new DateTime(2017, 1, 2), AccessTime= DateTime.Now.AddMinutes(1)},
    new Event(){Id=4,Emp ="A",EventDate= new DateTime(2017, 1, 3), AccessTime= DateTime.Now},
    new Event(){Id=5,Emp ="A",EventDate= new DateTime(2017, 1, 3), AccessTime= DateTime.Now.AddMinutes(2)},
    new Event(){Id=6,Emp ="A",EventDate= new DateTime(2017, 1, 3), AccessTime= DateTime.Now.AddMinutes(3)},
    new Event(){Id=7,Emp ="B",EventDate= new DateTime(2017, 2, 2), AccessTime= DateTime.Now},
    new Event(){Id=8,Emp ="B",EventDate= new DateTime(2017, 2, 2), AccessTime= DateTime.Now.AddMinutes(1)},
    new Event(){Id=9,Emp ="B",EventDate= new DateTime(2017, 2, 2), AccessTime= DateTime.Now.AddMinutes(2)}
};

如何使用最新的EventDate和AccessTime获取Emps？首先，使用最新的EventDate获取项目。如果EventDates相同，则获取具有最新AccessTime的项目。对于此列表，结果应为事件6和9.

Answer 1

您要找的是OrderBy和ThenBy。如果你的例子：

events.OrderByDescending(x => x.EventDate)
    .ThenByDescending(x => x.AccessTime);

这会先按最新events排序EventDate，然后按AccessTime排序（如果多个日期匹配）。

结果将包含ID 9，后跟8，因为它们具有最新的EventDate，而两个ID 9中的最新AccessTime。

Dotnet Fiddle

Answer 2

这会给你你想要的东西：

var result = events.GroupBy(x => x.Emp).Select(y => y.OrderByDescending(z => z.EventDate).ThenByDescending(q => q.AccessTime).First());
foreach (Event a in result)
{
            Console.WriteLine(a.Id + "\t" + a.Emp + "\t" + a.EventDate + "\t" + a.AccessTime);
}

首先，您需要Emp GroupBy，而不是OrderByDescending EventDate之前的订单组，而不是AccessTime和选择第一行。

最终结果将是：

9
6

Linq查询Sub / Group max两次

2 个答案: