Linq子查询 - 带

-1

处理一个有关赛马数据的问题。喜欢这里：Linq子查询 - 带

 outingsData = new List<RPOutingFull>(); 
     outingsData.Add(new RPOutingFull() { ID = 1, HorseID = hid1, FinishPositionVal = winPos, theDate = outingsStartDate.AddDays(-5) }); 
     outingsData.Add(new RPOutingFull() { ID = 2, HorseID = hid1, FinishPositionVal = winPos, theDate = outingsStartDate.AddDays(-4) }); 
     outingsData.Add(new RPOutingFull() { ID = 99, HorseID = 2, FinishPositionVal = winPos, theDate = outingsStartDate.AddDays(-4) }); 
     outingsData.Add(new RPOutingFull() { ID = 3, HorseID = hid1, FinishPositionVal = 3, theDate = outingsStartDate.AddDays(-1) }); 
     outingsData.Add(new RPOutingFull() { ID = 4, HorseID = hid1, FinishPositionVal = 3, theDate = outingsStartDate.AddDays(+1) }); 
     outingsData.Add(new RPOutingFull() { ID = 5, HorseID = hid1, FinishPositionVal = 6, theDate = outingsStartDate.AddDays(+4) }); 
     outingsData.Add(new RPOutingFull() { ID = 6, HorseID = hid1, FinishPositionVal = winPos, theDate = outingsStartDate.AddDays(+5) }); 
     outingsData.Add(new RPOutingFull() { ID = 7, HorseID = hid1, FinishPositionVal = winPos, theDate = outingsStartDate.AddDays(+22) }); 
     outingsData.Add(new RPOutingFull() { ID = 8, HorseID = 3, FinishPositionVal = winPos, theDate = outingsStartDate.AddDays(+22) }); 
     outingsData.Add(new RPOutingFull() { ID = 9, HorseID = 5, FinishPositionVal = 2, theDate = outingsStartDate.AddDays(+27) }); 
     outingsData.Add(new RPOutingFull() { ID = 10, HorseID = 5, FinishPositionVal = 4, theDate = outingsStartDate.AddDays(+55) }); 
     outingsData.Add(new RPOutingFull() { ID = 11, HorseID = 5, FinishPositionVal = 4, theDate = outingsStartDate.AddDays(+56) }); 
     outingsData.Add(new RPOutingFull() { ID = 12, HorseID = 5, FinishPositionVal = 5, theDate = outingsStartDate.AddDays(+95) }); 
     outingsData.Add(new RPOutingFull() { ID = 13, HorseID = 5, FinishPositionVal = 6, theDate = outingsStartDate.AddDays(+96) });

我想写一个LINQ查询 - 提供一个谓词选择在数据的初始项目，然后对每个符合条件的马

一个例子返回后续的X记录;给定该数据，和具有FinishPositionVal = 3的初始项目的谓词，并考虑随后的郊游的2对所有匹配跑者...应的ID 4,5,6

 // take next 2 outings 
     int takeCount = 2; 
     Predicate<RPOutingFull> predicate = full => full.FinishPositionVal == 3; 

     var resAllSubsequentOutings = (from s1 in outingsData 
        from s2 in outingsData 
        where 
        s2.theDate > s1.theDate && s1.HorseID == s2.HorseID && 
        predicate(s1) 
        orderby s1.theDate 
        select s2);

该部分返回返回项所有后续的出场，其中最初的谓词匹配。我可以将这个回归集合在一起，并从每个亚军身上拿走最高的x ..但那不正确。因为......谓词独立地从数据中的两个独立点开始：从ID3,4（其中位置= 3）开始，所以应该是从每个点开始2个随后的外出......即ID4， 5应该由于ID3匹配谓词而拾取，并且由于ID4匹配谓词而拾取ID5,6 ...然后4,5,5,6个不同应该留下4,5,6 ....

 CollectionAssert.AreEquivalent(new List<long>() { 4, 5, 6 }, resMissingQuery.Select(o => o.ID));

感谢

来源

2014-12-13 Hoo Man

找到了解决这个从适应查询后： http://stackoverflow.com/questions/880665/stuck-on -a-子查询 - 即-是-分组功能于LINQ – 2014-12-13 20:32:38

解决方案：VAR q =（从S1在outingsData 从克（从S2在outingsData 其中 s2.theDate> s1.theDate && s1.HorseID = = s2.HorseID && 谓词（s1） order by s1.theDate select s2）.Take（takeCount） select g）.Distinct ）.ToList（）; – 2014-12-13 20:33:05

我想重新写这个作为一个连接查询来提高性能....那不是那么容易。任何帮助赞赏。 – 2014-12-14 00:38:49

马特柯联接查询我想出是：

 Predicate<RPOutingWithNoComment> predicate = r => r.FinishPositionVal == 3; 
     var res = (from s1 in _testData 
        join s2 in _testData on s1.HorseID equals s2.HorseID 
        where s2.theDate > s1.theDate && 
         s1.HorseID == s2.HorseID && predicate(s1) 
        orderby s2.theDate 
        select s2).Distinct();

这部作品让后续的运行中，现在我想限制结果集仅在初始运行谓词选择运行之后接下来的两次运行。我知道，只获得排位赛之后的下一次运行，我可以使用：

 var q = from r in res 
      group r by r.HorseID 
      into g 
      select g.OrderBy(o => o.theDate).First();

来源

2014-12-15 22:56:03

Linq子查询 - 带

回答

相关问题