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


The .NET API Reference documentation has a new home. Visit the .NET API Browser on docs.microsoft.com to see the new experience.

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)

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


Type: System.Linq.IQueryable(Of TSource)

A sequence to aggregate over.

Type: TAccumulate

The initial accumulator value.

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.

Type Parameters


The type of the elements of source.


The type of the accumulator value.

Exception Condition

source or func is null.

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(Of TSource) and LongCount(Of TSource), and four numeric aggregation methods, namely Max(Of TSource), Min(Of TSource), 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 

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.1
Windows Phone
Available since 8.1
Return to top