如何在Linq GroupBy中選擇前N行

Question

希望你能在這里幫助我。 我有一個預訂清單，我希望在這些清單中獲得每組TourOperators的前2行。

這是數據示例：

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" });

我有這個Linq，但是它只給我每個組中的第一個Booking：

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

我希望的數據是這樣的：

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

謝謝。

Answer 1

用Take(2)替換First()並使用SelectMany() ：

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

更新 ：第一次忘記SelectMany 。 您想展平結果（ SelectMany這樣做），否則您將獲得IEnumerables列表。

Answer 2

嘗試使用var並將First()替換為Take(2) ：

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