Partager via

  • Article

Enumerable.Aggregate<TSource, TAccumulate> Method (IEnumerable<TSource>, TAccumulate, Func<TAccumulate, TSource, TAccumulate>)

Microsoft Silverlight will reach end of support after October 2021. Learn more.

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)

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function Aggregate(Of TSource, TAccumulate) ( _
    source As IEnumerable(Of TSource), _
    seed As TAccumulate, _
    func As Func(Of TAccumulate, TSource, TAccumulate) _
) As TAccumulate

public static TAccumulate Aggregate<TSource, TAccumulate>(
    this IEnumerable<TSource> source,
    TAccumulate seed,
    Func<TAccumulate, TSource, TAccumulate> func
)

Type Parameters

  • TSource
    The type of the elements of source.
  • TAccumulate
    The type of the accumulator value.

Parameters

  • seed
    Type: TAccumulate
    The initial accumulator value.
  • func
    Type: System.Func<TAccumulate, TSource, TAccumulate>
    An accumulator function to be invoked 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 IEnumerable<TSource>. When you use instance method syntax to call this method, omit the first parameter.

Exceptions

Exception Condition
ArgumentNullException

source or func is nulla null reference (Nothing in Visual Basic).

Remarks

The Aggregate<TSource, TAccumulate>(IEnumerable<TSource>, TAccumulate, Func<TAccumulate, TSource, TAccumulate>) 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<TSource, TAccumulate>(IEnumerable<TSource>, TAccumulate, Func<TAccumulate, TSource, TAccumulate>) 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<TSource, TAccumulate>(IEnumerable<TSource>, TAccumulate, Func<TAccumulate, TSource, TAccumulate>) 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.

Examples

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

   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 = _
          ints.Aggregate(0, _
                         Function(total, number) _
                             IIf(number Mod 2 = 0, total + 1, total))

      ' Display the output.
      outputBlock.Text &= "The number of even integers is " & numEven & vbCrLf
   End Sub

   ' This code produces the following output:
   '
   'The number of even integers is 6


      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);

      outputBlock.Text += String.Format("The number of even integers is: {0}", numEven) + "\n";

      // This code produces the following output:
      //
      // The number of even integers is: 6

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.