Queryable.Sum(Of TSource) Method (IQueryable(Of TSource), Expression(Of Func(Of TSource, Int64)))
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Computes the sum of the sequence of Int64 values that is obtained by invoking a projection function on each element of the input sequence.
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, Long)) _ ) As Long
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, Int64))
A projection function to apply to each element.
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.| Exception | Condition |
|---|---|
| ArgumentNullException | source or selector is Nothing. |
| OverflowException | The sum is larger than MaxValue. |
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, Int64))) method generates a MethodCallExpression that represents calling Sum(Of TSource)(IQueryable(Of TSource), Expression(Of Func(Of TSource, Int64))) 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, Int64))) 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.
Note: |
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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) 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
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