Question

例如，我有以下PlanesLogRow对象列表

public class PlanesLogRow
{
    public DateTime ArriveDate;
    public string Origin;
    public string Destination;
}

需要获取所有机场的列表(Origin + Destination).Distinct()
每个机场需要计算一次＃34;到达机场＆＃34;和＃34;离开机场＆＃34;计数。

我需要创建一个像<airport, AsOriginCount(arrivedToCount), AsDestinationCount(LeftFromCount)>

获取所有机场的列表并不是一个问题，但不确定如何通过不同的参数进行这种双重分组

Answer 1

如果您有飞机列表，则可以将每个飞机对象投影为两个匿名对象 - 一个用于目标，一个用于原点。然后按机场对这些匿名对象进行分组并计算总数：

planes.SelectMany(p => new[] { 
         new { Airport = p.origin, IsOrigin = true },
         new { Airport = p.destination, IsOrigin = false }
       })
       .GroupBy(x => x.Airport)
       .Select(g => new {
           Airport = g.Key,
           AsOriginCount = g.Count(x => x.IsOrigin),
           AsDestinationCount = g.Count(x => !x.IsOrigin)
       })

对于特定的飞机：

var planes = new List<Plane> {
    new Plane { Origin = "Minsk", Destination = "London" },
    new Plane { Origin = "Barcelona", Destination = "Minsk" },
    new Plane { Origin = "Rome", Destination = "Minsk" },
    new Plane { Origin = "Barcelona", Destination = "London" },
    new Plane { Origin = "London", Destination = "Rome" },
};

输出将是：

[
  { "Airport": "Minsk", "AsOriginCount": 1, "AsDestinationCount": 2 },
  { "Airport": "London", "AsOriginCount": 1, "AsDestinationCount": 2 },
  { "Airport": "Barcelona", "AsOriginCount": 2, "AsDestinationCount": 0 },
  { "Airport": "Rome", "AsOriginCount": 1, "AsDestinationCount": 1 }
]

更新：此查询将与Entity Framework一起使用。生成的SQL会很大而且很可怕。

LINQ - 具有元素计数的双重分组

1 个答案: