vb.net - 如何在多个 List(of) 中找到共同元素？

Question

我有如下三个列表

Dim foodList1 As New List(Of Food)
Dim foodList2 As New List(Of Food)
Dim foodList3 As New List(Of Food)

Dim resualt = From c In db.Food
              Where c.Code = X
              Select c

m_FoodList1 = resualt.ToList

我需要创建一个新列表，其中包含这三个列表共有的食物。有没有我可以使用的方法而不是通过列表并比较它们？提前谢谢你

Answer 1

您可以使用 Intersect()为此目的的方法。这适用于内部的 HashSet，因此它的性能非常好:

Dim result = foodList1.Intersect(foodList2).Intersect(foodList3)

如果 Food 类还没有覆盖 Equals 和 GetHashCode，您可以创建一个特殊的 IEqualityComparer并将其作为参数提供给 Intersect :

Class FoodEqualityComparer
    Implements IEqualityComparer(Of Food)

    Public Function Equals(x As Food, y As Food) As Boolean Implements IEqualityComparer(Of Food).Equals
        Return x.Code = y.Code
    End Function

    Public Function GetHashCode(x As Food) As Integer Implements IEqualityComparer(Of Food).GetHashCode
        Return x.Code.GetHashCode()
    End Function
End Class

' ...

Dim eqComp As New FoodEqualityComparer()
Dim result = foodList1.Intersect(foodList2, eqComp).Intersect(foodList3, eqComp)