使用LINQ查询对数据进行分组

Question

我有一个包含5列的C# DataTable。我只关心其中的两列，它们分别叫做“CreateDate”和“ID”。它们分别是DateTime和string类型。DateTime表示提交工单的日期，而ID唯一地标识了一个工单。

我想编写一个LINQ语句，以显示每个日期创建的工单数。但是，我无法弄清楚如何实现。是否有人可以向我展示如何做到这一点？

谢谢！

- user336786

Answer 1

我认为这样做是可行的：

var result = from ticket in TicketTable
group ticket by ticket.CreateDate.Date into g
select new {Date = g.Key, Count = g.Count() };

- recursive

---

+1. 正确的解决方案，假设 CreateDate 不包含精确时间。 - Niels van der Rest

CreateDate是一个完整的DateTime对象。如何解决这个问题？ - user336786

我的解决方案使用 .Date 来处理这个问题。 http://msdn.microsoft.com/zh-cn/library/system.datetime.date.aspx - recursive

Answer 2

class Program
{
    static void Main(string[] args)
    {
        List<Ticket> tickets = new List<Ticket>();

        tickets.Add(new Ticket() { CreateDate = DateTime.Now, Id = 1 });
        tickets.Add(new Ticket() { CreateDate = DateTime.Now.AddDays(1), Id = 2 });
        tickets.Add(new Ticket() { CreateDate = DateTime.Now.AddDays(1), Id = 3 });
        tickets.Add(new Ticket() { CreateDate = DateTime.Now.AddDays(2), Id = 4 });
        tickets.Add(new Ticket() { CreateDate = DateTime.Now.AddDays(2), Id = 5 });
        tickets.Add(new Ticket() { CreateDate = DateTime.Now.AddDays(3), Id = 6 });
        tickets.Add(new Ticket() { CreateDate = DateTime.Now.AddDays(3), Id = 7 });
        tickets.Add(new Ticket() { CreateDate = DateTime.Now.AddDays(4), Id = 8 });
        tickets.Add(new Ticket() { CreateDate = DateTime.Now.AddDays(5), Id = 9 });
        tickets.Add(new Ticket() { CreateDate = DateTime.Now.AddDays(6), Id = 10 });
        tickets.Add(new Ticket() { CreateDate = DateTime.Now.AddDays(7), Id = 11 });

        var query = tickets.
                    GroupBy(t => t.CreateDate.Date).
                    Select(g => new { Date = g.Key, Count = g.Count() });

        foreach (var g in query)
        {
            Console.WriteLine("{0} - {1}", g.Date, g.Count);
        }

        /* Outputs:
            7/24/2010 12:00:00 AM - 1
            7/25/2010 12:00:00 AM - 2
            7/26/2010 12:00:00 AM - 2
            7/27/2010 12:00:00 AM - 2
            7/28/2010 12:00:00 AM - 1
            7/29/2010 12:00:00 AM - 1
            7/30/2010 12:00:00 AM - 1
            7/31/2010 12:00:00 AM - 1 */
    }

    class Ticket
    {
        public int Id { get; set; }
        public DateTime CreateDate { get; set; }
    }
}

- Leniel Maccaferri