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

Applies an accumulator function over a sequence.

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

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

source
Type: System.Collections.Generic.IEnumerable<TSource>

An IEnumerable<T> to aggregate over.

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. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).

ExceptionCondition
ArgumentNullException

source or func is null.

InvalidOperationException

source contains no elements.

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.

The following code example demonstrates how to use Aggregate to build a sentence from an array of strings.

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);

Console.WriteLine(reversed);

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

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5

.NET Compact Framework

Supported in: 3.5

XNA Framework

Supported in: 3.0
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