Question

我编写了以下通用LINQ扩展来计算Visual Basic 2010中的加权平均值：

<Extension()>
Function WeightedAverage(Of T)(ByVal source As IEnumerable(Of T),
              ByVal selectorValue As Func(Of T, Integer),
              ByVal selectorWeight As Func(Of T, Integer)) As Double
  Dim weightedValueSum As Double
  Dim weightSum As Integer

  weightedValueSum = (From element In source
                      Select (selectorValue(element) * selectorWeight(element))).Sum()
  weightSum = (From element In source
               Select selectorWeight(element)).Sum()
  If weightSum <> 0 Then
      Return weightedValueSum / weightSum
  Else
      Return 0
  End If
End Function

如何将此函数作为另一个LINQ查询的聚合函数调用？

我按照以下方式尝试了它：

Dim q1 = From jd In oContext.JobDatas
         Where jd.Year = 2011
         Select jd
Dim q2 = Aggregate num In q1 Into WeightedAverage(num.AvSalary, num.NumPosHolder)

Visual Basic 2010编辑器告诉我以下代码的第二个查询（q2）不是有效语句。在第一个第二个参数之间的逗号，它说：“）”必需。怎么了？

Answer 1

使用聚合函数有什么特别的理由吗？如果您只想计算第一个查询的加权平均值，则可以执行以下操作：

Dim q1 = From jd In oContext.JobDatas
         Where jd.Year = 2011
         Select jd
Dim avg As Double = q1.WeighedAverage(Function(num) num.AvSalary, Function(num) num.NumPosHolder)

用于在Visual Basic 2010中计算加权平均值的通用LINQ扩展

1 个答案: