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


Applies an accumulator function over a sequence. The specified seed value is used as the initial accumulator value, and the specified function is used to select the result value.

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

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


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

An IEnumerable<T> to aggregate over.

Type: TAccumulate

The initial accumulator value.

Type: System.Func<TAccumulate, TSource, TAccumulate>

An accumulator function to be invoked on each element.

Type: System.Func<TAccumulate, TResult>

A function to transform the final accumulator value into the result value.

Return Value

Type: TResult

The transformed final accumulator value.

Type Parameters


The type of the elements of source.


The type of the accumulator value.


The type of the resulting value.

Exception Condition

source or func or resultSelector is null.

The Aggregate<TSource, TAccumulate, TResult>(IEnumerable<TSource>, TAccumulate, Func<TAccumulate, TSource, TAccumulate>, Func<TAccumulate, TResult>) 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, TResult>(IEnumerable<TSource>, TAccumulate, Func<TAccumulate, TSource, TAccumulate>, Func<TAccumulate, TResult>) 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. The final result of func is passed to resultSelector to obtain the final result of Aggregate<TSource, TAccumulate, TResult>(IEnumerable<TSource>, TAccumulate, Func<TAccumulate, TSource, TAccumulate>, Func<TAccumulate, TResult>).

To simplify common aggregation operations, the standard query operators also include a general purpose count method, Count<TSource>, and four numeric aggregation methods, namely Min, Max, Sum, and Average.

The following code example demonstrates how to use Aggregate<TSource, TAccumulate, TResult> to apply an accumulator function and a result selector.

string[] fruits = { "apple", "mango", "orange", "passionfruit", "grape" };

// Determine whether any string in the array is longer than "banana".
string longestName =
                    (longest, next) =>
                        next.Length > longest.Length ? next : longest,
    // Return the final result as an upper case string.
                    fruit => fruit.ToUpper());

    "The fruit with the longest name is {0}.",

// This code produces the following output:
// The fruit with the longest name is PASSIONFRUIT. 

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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