如何根据 属性 获得两个 类 的交集

Question

我有这个class

public class FlightSegment{
     public string ClassName { get;set;}
}

我想用普通的 ClassName

得到 FlightSegments

void Main()
{
    var list1 = new List<FlightSegment>() { 
        new FlightSegment{ ClassName = "A"},
        new FlightSegment { ClassName = "B"}
    };      
    var list2 = new List<FlightSegment>() { 
        new FlightSegment{ ClassName = "B"},
        new FlightSegment { ClassName = "C"}
    }; 

    var listOfLists = new List<List<FlightSegment>>() { list1, list2 };     
    var intersection = listOfLists.Aggregate((previousList, nextList) => previousList.Intersect(nextList).ToList());        
    Console.WriteLine(intersection); //Gives me empty result

}

我试过这样的事情：

    var intersection = listOfLists.Aggregate((previousList, nextList) =>   
      previousList.Select(e=>e.ClassName).Intersect(nextList.Select(e=>e.ClassName)).ToList());

但是报错：

Cannot convert expression type System.Collection.Generic.List<string> to return type System.Collection.Generic.List<FlightSegment>

Answer 1

可以用Intersect method passing a IEqualityComparer根据ClassName比较属性:

class FlightComparer : EqualityComparer<FlightSegment>
{
    public override bool Equals(FlightSegment x, FlightSegment y)
    {
        return x.ClassName == y.ClassName;
    }

    public override int GetHashCode(FlightSegment obj)
    {
        return obj.ClassName.GetHashCode();
    }
}

然后，使用这个比较器进行交集：

var list1 = new List<FlightSegment>() { 
    new FlightSegment{ ClassName = "A"},
    new FlightSegment { ClassName = "B"}
};      
var list2 = new List<FlightSegment>() { 
    new FlightSegment{ ClassName = "B"},
    new FlightSegment { ClassName = "C"}
}; 
var result = list1.Intersect(list2, new FlightComparer());

这个returns一个只包含一个元素的集合FlightSegment { ClassName = "B" }。

利用这个思路和Aggregate，可以得到一组基于属性:

的列表的交集

var intersection = listOfLists.Aggregate((previousList, nextList) => previousList.Intersect(nextList, new FlightComparer() ).ToList());