如何在Linq GroupBy中选择前N行

希望你能在这里帮助我。 我有一个预订列表，我想在每组TourOperators中获得前两行。

这是一个数据样本：

List list = new List(); list.Add(new Booking() { BookingNo = "31111111", DepDate = new DateTime(2011, 5, 1), TourOperator = "SPI" }); list.Add(new Booking() { BookingNo = "32222222", DepDate = new DateTime(2011, 5, 2), TourOperator = "SPI" }); list.Add(new Booking() { BookingNo = "33333333", DepDate = new DateTime(2011, 5, 3), TourOperator = "SPI" }); list.Add(new Booking() { BookingNo = "34444444", DepDate = new DateTime(2011, 5, 4), TourOperator = "SPI" }); list.Add(new Booking() { BookingNo = "35555555", DepDate = new DateTime(2011, 5, 5), TourOperator = "SPI" }); list.Add(new Booking() { BookingNo = "36666666", DepDate = new DateTime(2011, 5, 6), TourOperator = "SPI" }); list.Add(new Booking() { BookingNo = "11111111", DepDate = new DateTime(2011, 5, 1), TourOperator = "VIN" }); list.Add(new Booking() { BookingNo = "12222222", DepDate = new DateTime(2011, 5, 2), TourOperator = "VIN" }); list.Add(new Booking() { BookingNo = "13333333", DepDate = new DateTime(2011, 5, 3), TourOperator = "VIN" }); list.Add(new Booking() { BookingNo = "14444444", DepDate = new DateTime(2011, 5, 4), TourOperator = "VIN" }); list.Add(new Booking() { BookingNo = "15555555", DepDate = new DateTime(2011, 5, 5), TourOperator = "VIN" }); list.Add(new Booking() { BookingNo = "16666666", DepDate = new DateTime(2011, 5, 6), TourOperator = "VIN" }); list.Add(new Booking() { BookingNo = "17777777", DepDate = new DateTime(2011, 5, 7), TourOperator = "VIN" }); 

我有这个Linq，但它只给了我每组的第一个预订：

 List yetAnotherList = list.GroupBy(row => row.TourOperator) .Select(g => g.OrderBy(row => row.DepDate).First()).ToList(); 

我希望的数据是这样的：

31111111,2011-05-01，SPI
32222222,2011-05-02，SPI
11111111,2011-05-01，VIN
12222222,2011-05-02，VIN

谢谢。

Answer 1

用Take(2)替换First()并使用SelectMany() ：

 List yetAnotherList = list.GroupBy(row => row.TourOperator) .SelectMany(g => g.OrderBy(row => row.DepDate).Take(2)) .ToList(); 

更新 ：第一次忘记SelectMany 。 您希望展平结果（ SelectMany ），否则您将获得IEnumerables列表。

Answer 2

尝试使用var并将Take(2)替换为Take(2) ：

 var yetAnotherList = list.GroupBy(row => row.TourOperator) .Select(g => g.OrderBy(row => row.DepDate).Take(2)).ToList();