EnumerableAggregate Method

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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 static TAccumulate Aggregate<TSource, TAccumulate>(
	this IEnumerable<TSource> source,
	TAccumulate seed,
	Func<TAccumulate, TSource, TAccumulate> func
generic<typename TSource, typename TAccumulate>
static TAccumulate Aggregate(
	IEnumerable<TSource>^ source,
	TAccumulate seed,
	Func<TAccumulate, TSource, TAccumulate>^ func
static member Aggregate<'TSource, 'TAccumulate> : 
        source:IEnumerable<'TSource> *
        seed:'TAccumulate *
        func:Func<'TAccumulate, 'TSource, 'TAccumulate> -> 'TAccumulate
Public Shared Function Aggregate(Of TSource, TAccumulate) (
	source As IEnumerable(Of TSource),
	seed As TAccumulate,
	func As Func(Of TAccumulate, TSource, TAccumulate)
) As TAccumulate



An IEnumerable to aggregate over.

Type: TAccumulate

The initial accumulator value.


An accumulator function to be invoked 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.

The Aggregate method makes it simple to perform a calculation over a sequence of values. This method works by calling func one time for each element in source. Each time func is called, Aggregate passes both the element from the sequence and an aggregated value (as the first argument to func). The value of the seed parameter is used as the initial aggregate value. The result of func replaces the previous aggregated value. Aggregate returns the final result of func.

To simplify common aggregation operations, the standard query operators also include a general purpose count method, Count, and four numeric aggregation methods, namely Min, Max, Sum, and Average.

The following code example demonstrates how to use Aggregate to apply an accumulator function and use a seed value.

int[] ints = { 4, 8, 8, 3, 9, 0, 7, 8, 2 };

// Count the even numbers in the array, using a seed value of 0.
int numEven = ints.Aggregate(0, (total, next) =>
                                    next % 2 == 0 ? total + 1 : total);

Console.WriteLine("The number of even integers is: {0}", numEven);

// This code produces the following output:
// The number of even integers is: 6 
Sub AggregateEx2()
    ' Create an array of Integers.
    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 =
                   Function(ByVal total, ByVal number) _
                       IIf(number Mod 2 = 0, total + 1, total))

    ' Display the output.
    MsgBox("The number of even integers is " & numEven)
End Sub

' 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 7.0
Windows Phone
Available since 8.1
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