Question

我有一个列表的代码，我可以在列表中有重复的记录。在最终结果中，我需要删除重复的条目并使它们唯一。我编写了如下代码，

public class BusLocation
{
    public string Latitude { get; set; }
    public string Longitude { get; set; }

    public string BusNumber { get; set; }
    public Int64 ScheduleId { get; set; }
    public Int64 TripId { get; set; }
}

List<BusLocation> _BusLocation=new List<BusLocation>();
BusLocation loc = new BusLocation();
loc.BusNumber = "123";
loc.Latitude = "12.1234";
loc.Longitude = "44.1234";
loc.ScheduleId = 77;
loc.TripId = 1678;

_BusLocation.Add(loc);

loc.BusNumber = "123";
loc.Latitude = "12.1234";
loc.Longitude = "44.1234";
loc.ScheduleId = 77;
loc.TripId = 1678;

_BusLocation.Add(loc);

loc.BusNumber = "123";
loc.Latitude = "12.1334";
loc.Longitude = "44.1334";
loc.ScheduleId = 78;
loc.TripId = 1679;

_BusLocation.Add(loc);
var result1 = _BusLocation
    .GroupBy(lat => lat.Latitude)
    .Select(grp => grp.ToList())
    .ToList();

但它给了我错误的结果，因为最后的记录重复了3次，我希望列表中的输出为

loc.BusNumber = "123";
loc.Latitude = "12.1234";
loc.Longitude = "44.1234";
loc.ScheduleId = 77;
loc.TripId = 1678;

loc.BusNumber = "123";
loc.Latitude = "12.1334";
loc.Longitude = "44.1334";
loc.ScheduleId = 78;
loc.TripId = 1679;

欢迎任何建议。

Answer 1

您的代码有错误。不是向列表中添加三个不同的BusLocation实例，而是将相同的实例添加三次。您可以使用初始化程序修复代码并使其更简洁：

List<BusLocation> _BusLocation = new List<BusLocation>() {
  new BusLocation {
    BusNumber = "123",
    Latitude = "12.1234",
    Longitude = "44.1234",
    ScheduleId = 77,
    TripId = 1678
  },
  new BusLocation {
    Latitude = "12.1234",
    Longitude = "44.1234",
    ScheduleId = 77,
    TripId = 1678
  },
  new BusLocation {
    BusNumber = "123",
    Latitude = "12.1334",
    Longitude = "44.1334",
    ScheduleId = 78,
    TripId = 1679
  }
};

要删除重复项，您需要定义重复项。您可以通过创建IEqualityComparer<BusLocation>类：

来实现

class BusLocationEqualityComparer : IEqualityComparer<BusLocation> {

  public Boolean Equals(BusLocation x, BusLocation y) {
    return x.BusNumber == y.BusNumber
      && x.Latitude == y.Latitude
      && x.Longitude == y.Longitude;
  }

  public Int32 GetHashCode(BusLocation obj) {
    unchecked {
      const Int32 Multiplier = -1521134295;
      var hash = -1901080290;
      hash = hash*Multiplier + obj.Latitude?.GetHashCode() ?? 0;
      hash = hash*Multiplier + obj.Longitude?.GetHashCode() ?? 0;
      hash = hash*Multiplier + obj.BusNumber?.GetHashCode() ?? 0;
      return hash;
    }
  }

}

此处，等式定义为具有相同的总线编号，纬度和经度。但是，当你使用字符串表示纬度和经度时，我不确定它是否会起作用，但我会把它留给你。

要获得不同的总线位置，您可以使用LINQ：

var distinctBusLocations = _BusLocation.Distinct(new BusLocationEqualityComparer());

Answer 2

我建议你使用Distinct（）函数。 https://msdn.microsoft.com/library/bb348436(v=vs.100).aspx

它看起来像这样：

SELECT e.id, e.name, e.salary, e.did, d.dname
FROM [dbo].[Table_1] e , [dbo].[Table_2] d
WHERE  e.did = d.did
GROUP BY e.id, e.name, e.salary, e.did, d.dname;

通过使用Linq从列表

2 个答案: