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Enumerable.Sum(Of TSource) Method (IEnumerable(Of TSource), Func(Of TSource, Nullable(Of Single)))

Computes the sum of the sequence of nullable Single 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)

<ExtensionAttribute> _
Public Shared Function Sum(Of TSource) ( _
	source As IEnumerable(Of TSource), _
	selector As Func(Of TSource, Nullable(Of Single)) _
) As Nullable(Of Single)
Dim source As IEnumerable(Of TSource)
Dim selector As Func(Of TSource, Nullable(Of Single))
Dim returnValue As Nullable(Of Single)

returnValue = source.Sum(selector)

Type Parameters


The type of the elements of source.


Type: System.Collections.Generic.IEnumerable(Of TSource)

A sequence of values that are used to calculate a sum.

Type: System.Func(Of TSource, Nullable(Of Single))

A transform function to apply to each element.

Return Value

Type: System.Nullable(Of Single)
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. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).


source or selector is Nothing.

This method returns zero if source contains no elements.

The result does not include values that are Nothing.

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 Nullable<Single> in C# or Nullable(Of Single) in Visual Basic.

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

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.


This code example uses an overload of this overloaded method that is different from the specific overload that this topic describes. To extend the example to this topic, change the body of the selector function.

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) _

    ' Display the result.
    MsgBox("The total weight of the packages is: " & totalWeight)
End Sub 

' This code produces the following output: 

' The total weight of the packages is: 83.7

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5

.NET Compact Framework

Supported in: 3.5

XNA Framework

Supported in: 3.0