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Enumerable.Sum(Of TSource) Method (IEnumerable(Of TSource), Func(Of TSource, Double))

Silverlight

Computes the sum of the sequence of Double values that are obtained by invoking a transform function on each element of the input sequence.

Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function Sum(Of TSource) ( _
	source As IEnumerable(Of TSource), _
	selector As Func(Of TSource, Double) _
) As Double

Type Parameters

TSource: The type of the elements of source.

Parameters

source: Type: System.Collections.Generic.IEnumerable(Of TSource)
A sequence of values that are used to calculate a sum.

selector: Type: System.Func(Of TSource, Double)
A transform function to apply to each element.

Return Value

Type: System.Double
The sum of the projected values.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable(Of TSource). When you use instance method syntax to call this method, omit the first parameter.

Exceptions

Exception	Condition
ArgumentNullException	source or selector is Nothing.

Remarks

This method returns zero if source contains no elements.

You can apply this method to a sequence of arbitrary values if you provide a function, selector, that projects the members of source into a numeric type, specifically Double.

In Visual Basic query expression syntax, an Aggregate Into Sum() clause translates to an invocation of Sum.

Examples

The following code example demonstrates how to use Sum(Of TSource)(IEnumerable(Of TSource), Func(Of TSource, Double)) to sum the projected values of a sequence.


   Structure Package
      Public Company As String
      Public Weight As Double
   End Structure

   Sub SumEx1()
      ' Create a list of Package values.
      Dim packages As New List(Of Package)(New Package() _
           {New Package With {.Company = "Coho Vineyard", .Weight = 25.2}, _
            New Package With {.Company = "Lucerne Publishing", .Weight = 18.7}, _
            New Package With {.Company = "Wingtip Toys", .Weight = 6.0}, _
            New Package With {.Company = "Adventure Works", .Weight = 33.8}})

      ' Sum the values from each item's Weight property.
      Dim totalWeight As Double = packages.Sum(Function(pkg) _
                                                   pkg.Weight)

      ' Display the result.
      outputBlock.Text &= "The total weight of the packages is: " & totalWeight & VbCrLf
   End Sub

   ' This code produces the following output:
   '
   ' The total weight of the packages is: 83.7