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如何按字段分组列表,并通过linq将另一个字段的min分组?

linq c#

hmahdavi · 技术社区 · 10 年前

我有一个航班列表,我试图用日期字段将其分组,然后在其中选择每个组的最低价格。我应该得到的结果每天最便宜的航班。

(from flights in aFlightList
                                   where flights.IsDeparture && flights.OnlyTour == "0" && flights.OnlyPhone == "0"
                                   group flights by flights.FlightDateFull
                                       into grouping
                                       select grouping.OrderBy(a => a.FlightDateFull).First()).ToArray();

此代码按日期分组列表,但无法获得最便宜的航班。

(from flights in aFlightList
                                   where flights.IsDeparture && flights.OnlyTour == "0" && flights.OnlyPhone == "0"
                                   group flights by flights.FlightDateFull
                                       into grouping
                                       select grouping.OrderBy(a => a.FlightDateFull).Min(d=>d.PriceView)).ToArray();

这样会出错。

如何做到这一点?

2 回复 | 直到 10 年前

Ivan Stoev 10 年前

的结果 group by 操作是分组列表,其中分组由一个键和共享该键的元素列表组成。

让我们来看看您的第一个查询。按操作分组 aFlightList 按日期,因此无需按日期对组元素进行进一步排序(相同)。但你可以按价格订购,所以 First 将以最低价格返回元素。最后,由于 分组依据 结果组可能不是您想要的,您可以订购分组通过键(或其部分)。

综上所述,修改后的查询可能如下:

(from flights in aFlightList
 where flights.IsDeparture && flights.OnlyTour == "0" && flights.OnlyPhone == "0"
 group flights by flights.FlightDateFull
 into grouping
 orderby grouping.Key
 select grouping.OrderBy(e => e.PriceView).First())
.ToArray();

Jeroen Heier 10 年前

您可以创建具有所需结果的新对象,并对其执行选择。例子:

    class Flight
    {
        public bool IsDeparture;
        public string OnlyTour;
        public string OnlyPhone;
        public DateTime FlightDateFull;
        public decimal PriceView;
    }

    [TestMethod]
    public void FlightTest()
    {
        // Arrange
        var flightList = new List<Flight> {
            new  Flight { IsDeparture = true, OnlyPhone = "0", OnlyTour = "0", FlightDateFull = new DateTime(2016,8,7), PriceView = 1 },
            new  Flight { IsDeparture = true, OnlyPhone = "0", OnlyTour = "0", FlightDateFull = new DateTime(2016,8,7), PriceView = 2 },
            new  Flight { IsDeparture = true, OnlyPhone = "0", OnlyTour = "0", FlightDateFull = new DateTime(2016,8,8), PriceView = 2 },
            new  Flight { IsDeparture = true, OnlyPhone = "0", OnlyTour = "0", FlightDateFull = new DateTime(2016,8,8), PriceView = 3 }
        };

        // Act
        var result = (from flights in flightList
                      where flights.IsDeparture && flights.OnlyTour == "0" && flights.OnlyPhone == "0"
                      group flights by flights.FlightDateFull into grouping
                      select new { Date = grouping.Key, MinPrice = grouping.Min(a => a.PriceView) }).OrderBy(a => a.Date).ToList();

        // Assert
        Assert.AreEqual(new DateTime(2016, 8, 7), result[0].Date);
        Assert.AreEqual(1, result[0].MinPrice);
        Assert.AreEqual(new DateTime(2016, 8, 8), result[1].Date);
        Assert.AreEqual(2, result[1].MinPrice);
    }