Enumerable.Aggregate(Of TSource, TAccumulate, TResult) Method (IEnumerable(Of TSource), TAccumulate, Func(Of TAccumulate, TSource, TAccumulate), Func(Of TAccumulate, TResult))

 

Applies an accumulator function over a sequence. The specified seed value is used as the initial accumulator value, and the specified function is used to select the result value.

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

<ExtensionAttribute>
Public Shared Function Aggregate(Of TSource, TAccumulate, TResult) (
	source As IEnumerable(Of TSource),
	seed As TAccumulate,
	func As Func(Of TAccumulate, TSource, TAccumulate),
	resultSelector As Func(Of TAccumulate, TResult)
) As TResult

Parameters

source
Type: System.Collections.Generic.IEnumerable(Of TSource)

An IEnumerable(Of T) to aggregate over.

seed
Type: TAccumulate

The initial accumulator value.

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

An accumulator function to be invoked on each element.

resultSelector
Type: System.Func(Of TAccumulate, TResult)

A function to transform the final accumulator value into the result value.

Return Value

Type: TResult

The transformed final accumulator value.

Type Parameters

TSource

The type of the elements of source.

TAccumulate

The type of the accumulator value.

TResult

The type of the resulting value.

Exception Condition
ArgumentNullException

source or func or resultSelector is null.

The Aggregate(Of TSource, TAccumulate, TResult)(IEnumerable(Of TSource), TAccumulate, Func(Of TAccumulate, TSource, TAccumulate), Func(Of TAccumulate, TResult)) 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(Of TSource, TAccumulate, TResult)(IEnumerable(Of TSource), TAccumulate, Func(Of TAccumulate, TSource, TAccumulate), Func(Of TAccumulate, TResult)) 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. The final result of func is passed to resultSelector to obtain the final result of Aggregate(Of TSource, TAccumulate, TResult)(IEnumerable(Of TSource), TAccumulate, Func(Of TAccumulate, TSource, TAccumulate), Func(Of TAccumulate, TResult)).

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

The following code example demonstrates how to use Aggregate(Of TSource, TAccumulate, TResult) to apply an accumulator function and a result selector.

Sub AggregateEx3()
    Dim fruits() As String =
    {"apple", "mango", "orange", "passionfruit", "grape"}

    ' Determine whether any string in the array is longer than "banana".
    Dim longestName As String =
    fruits.Aggregate("banana",
                     Function(ByVal longest, ByVal fruit) _
                         IIf(fruit.Length > longest.Length, fruit, longest),
                     Function(ByVal fruit) fruit.ToUpper())

    ' Display the output.
    MsgBox("The fruit with the longest name is " & longestName)
End Sub

' This code produces the following output:
'
' The fruit with the longest name is PASSIONFRUIT

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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