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Queryable.Aggregate(Of TSource, TAccumulate) Method (IQueryable(Of TSource), TAccumulate, Expression(Of Func(Of TAccumulate, TSource, TAccumulate)))

Applies an accumulator function over a sequence. The specified seed value is used as the initial accumulator value.

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

'Declaration
<ExtensionAttribute> _
Public Shared Function Aggregate(Of TSource, TAccumulate) ( _
	source As IQueryable(Of TSource), _
	seed As TAccumulate, _
	func As Expression(Of Func(Of TAccumulate, TSource, TAccumulate)) _
) As TAccumulate
'Usage
Dim source As IQueryable(Of TSource)
Dim seed As TAccumulate
Dim func As Expression(Of Func(Of TAccumulate, TSource, TAccumulate))
Dim returnValue As TAccumulate

returnValue = source.Aggregate(seed, _
	func)

Type Parameters

TSource

The type of the elements of source.

TAccumulate

The type of the accumulator value.

Parameters

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

A sequence to aggregate over.

seed
Type: TAccumulate

The initial accumulator value.

func
Type: System.Linq.Expressions.Expression(Of Func(Of TAccumulate, TSource, TAccumulate))

An accumulator function to invoke on each element.

Return Value

Type: TAccumulate
The final accumulator value.

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 func 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 Aggregate(Of TSource, TAccumulate)(IQueryable(Of TSource), TAccumulate, Expression(Of Func(Of TAccumulate, TSource, TAccumulate))) method generates a MethodCallExpression that represents calling Aggregate(Of TSource, TAccumulate)(IQueryable(Of TSource), TAccumulate, Expression(Of Func(Of TAccumulate, TSource, TAccumulate))) 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 Aggregate(Of TSource, TAccumulate)(IQueryable(Of TSource), TAccumulate, Expression(Of Func(Of TAccumulate, TSource, TAccumulate))) depends on the implementation of the type of the source parameter. The expected behavior is that the specified function, func, is applied to each value in the source sequence and the accumulated value is returned. The seed parameter is used as the seed value for the accumulated value, which corresponds to the first parameter in func.

To simplify common aggregation operations, the set of standard query operators also includes two counting methods, Count and LongCount, and four numeric aggregation methods, namely Max, Min, Sum, and Average.

The following code example demonstrates how to use Aggregate(Of TSource, TAccumulate)(IQueryable(Of TSource), TAccumulate, Expression(Of Func(Of TAccumulate, TSource, TAccumulate))) to apply an accumulator function when a seed value is provided to the function.

Dim ints() As Integer = {4, 8, 8, 3, 9, 0, 7, 8, 2}

' Count the even numbers in the array, using a seed value of 0. 
Dim numEven As Integer = _
    ints.AsQueryable().Aggregate( _
        0, _
        Function(ByVal total, ByVal number) _
            IIf(number Mod 2 = 0, total + 1, total) _
    )

MsgBox(String.Format("The number of even integers is: {0}", numEven))

' This code produces the following output: 

' The number of even integers is: 6 

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

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

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