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

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Applies an accumulator function over a sequence.

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

Syntax

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

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

Type Parameters

  • TSource
    The type of the elements of source.

Parameters

  • func
    Type: System.Func<TSource, TSource, TSource>
    An accumulator function to be invoked on each element.

Return Value

Type: TSource
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).
InvalidOperationException

source contains no elements.

Remarks

The Aggregate<TSource>(IEnumerable<TSource>, Func<TSource, TSource, TSource>) 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>(IEnumerable<TSource>, Func<TSource, TSource, TSource>) passes both the element from the sequence and an aggregated value (as the first argument to func). The first element of source is used as the initial aggregate value. The result of func replaces the previous aggregated value. Aggregate<TSource>(IEnumerable<TSource>, Func<TSource, TSource, TSource>) 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 build a sentence from an array of strings.

   Sub AggregateEx1()
      Dim sentence As String = _
          "the quick brown fox jumps over the lazy dog"
      ' Split the string into individual words.
      Dim words() As String = sentence.Split(" "c)
      ' Prepend each word to the beginning of the new sentence to reverse the word order.
      Dim reversed As String = _
          words.Aggregate(Function(current, word) word & " " & current)

      ' Display the output.
      outputBlock.Text += reversed + vbCrLf
   End Sub

   ' This code produces the following output:
   '
   ' dog lazy the over jumps fox brown quick the


      string sentence = "the quick brown fox jumps over the lazy dog";

      // Split the string into individual words.
      string[] words = sentence.Split(' ');

      // Prepend each word to the beginning of the 
      // new sentence to reverse the word order.
      string reversed = words.Aggregate((workingSentence, next) =>
                                            next + " " + workingSentence);

      outputBlock.Text += reversed + "\n";

      // This code produces the following output:
      //
      // dog lazy the over jumps fox brown quick the

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.