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

July 28, 2014

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)

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

source
Type: System.Collections.Generic.IEnumerable<TSource>
An IEnumerable<T> to aggregate over.
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.

ExceptionCondition
ArgumentNullException

source or func is null.

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.

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


      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 



Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

Show:
© 2014 Microsoft