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Queryable.Sum(Of TSource) Method (IQueryable(Of TSource), Expression(Of Func(Of TSource, Nullable(Of Double))))

Computes the sum of the sequence of nullable Double values that is obtained by invoking a projection function on each element of the input sequence.

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

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

Type Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Linq.IQueryable(Of TSource)

A sequence of values of type TSource.

selector
Type: System.Linq.Expressions.Expression(Of Func(Of TSource, Nullable(Of Double)))

A projection function to apply to each element.

Return Value

Type: System.Nullable(Of 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 IQueryable(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).

ExceptionCondition
ArgumentNullException

source or selector is Nothing.

This method has at least one parameter of type Expression(Of TDelegate) whose type argument is one of the Func(Of T, TResult) types. For these parameters, you can pass in a lambda expression and it will be compiled to an Expression(Of TDelegate).

The Sum(Of TSource)(IQueryable(Of TSource), Expression(Of Func(Of TSource, Nullable(Of Double)))) method generates a MethodCallExpression that represents calling Sum(Of TSource)(IQueryable(Of TSource), Expression(Of Func(Of TSource, Nullable(Of Double)))) itself as a constructed generic method. It then passes the MethodCallExpression to the Execute(Of TResult)(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

The query behavior that occurs as a result of executing an expression tree that represents calling Sum(Of TSource)(IQueryable(Of TSource), Expression(Of Func(Of TSource, Nullable(Of Double)))) depends on the implementation of the type of the source parameter. The expected behavior is that it invokes selector on each element of source and returns the sum of the resulting values.

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

NoteNote

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 

    Shared Sub SumEx3()
        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}})

        ' Calculate the sum of all package weights. 
        Dim totalWeight As Double = packages.AsQueryable().Sum(Function(pkg) pkg.Weight)

        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

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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