Question

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<Booking> list = new List<Booking>();
        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<Booking> 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

感谢。

Answer 1

将First()替换为Take(2)并使用SelectMany()：

List<Booking> 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执行此操作），否则您会得到IEnumerables的列表。

Answer 2

尝试使用var并将First()替换为Take(2)：

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

如何在Linq GroupBy中选择前N行

2 个答案: