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

Applies an accumulator function over a sequence.

Namespace:  System.Linq
Assemblies:   System.Linq (in System.Linq.dll)
  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 except the first one. 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.

This overload of the Aggregate method isn't suitable for all cases because it uses the first element of source as the initial aggregate value. You should choose another overload if the return value should include only the elements of source that meet a certain condition. For example, this overload isn't reliable if you want to calculate the sum of the even numbers in source. The result will be incorrect if the first element is odd instead of even.

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 reverse the order of words in a string by using Aggregate.

            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 

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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