Aggregate (LINQ)

Enumerable.Aggregate is C# version of fold or reduce function. It is extension method from System.Linq namespace.

Aggregate method applies a function to each item of a collection. For example, let's have collection { 6, 2, 8, 3 } and the function Add (operator +) it does (((6+2)+8)+3) and returns 19.

Aggregate alternative for Sum

Implementation of Sum using Aggregate method. This example use Aggregate method overload with only one parameter func. Into the func parameter there is passed lambda expression (anonymous method) which adds two numbers.

This example is for demonstration purpose only. To compute sum of numbers use rather Enumerable.Sum.

var numbers = new List<int> { 6, 2, 8, 3 }; int sum = numbers.Aggregate(func: (result, item) => result + item); // sum: (((6+2)+8)+3) = 19

In this example there is passed named method Add insted of lambda expression.

var numbers = new List<int> { 6, 2, 8, 3 }; int sum = numbers.Aggregate(func: Add); // sum: (((6+2)+8)+3) = 19

private static int Add(int x, int y) { return x + y; }

Aggregate alternative for Average

Implementation of Average using Aggregate method. There is used Aggregate method overload with three parameters, seed, func and resultSelector.

This example is for demonstration purpose only. To compute average value use rather Enumerable.Average.

var numbers = new List<int> { 6, 2, 8, 3 }; decimal average = numbers.Aggregate( seed: 0, func: (result, item) => result + item, resultSelector: result => (decimal)result / numbers.Count); // average: ((((0+6)+2)+8)+3) / 4 = 4.75

Aggregate Implementation

This is .NET Framework implementation of Enumerable.Aggregate method with only one paramater func.

public static TSource Aggregate<TSource>( this IEnumerable<TSource> source, Func<TSource, TSource, TSource> func) { if (source == null) throw Error.ArgumentNull("source"); if (func == null) throw Error.ArgumentNull("func"); using (IEnumerator<TSource> e = source.GetEnumerator()) { if (!e.MoveNext()) throw Error.NoElements(); TSource result = e.Current; while (e.MoveNext()) { result = func(result, e.Current); } return result; } }

This is .NET Framework implementation of Enumerable.Aggregate method with three parameters seed, func and resultSelector.

public static TResult Aggregate<TSource, TAccumulate, TResult>( this IEnumerable<TSource> source, TAccumulate seed, Func<TAccumulate, TSource, TAccumulate> func, Func<TAccumulate, TResult> resultSelector) { if (source == null) throw Error.ArgumentNull("source"); if (func == null) throw Error.ArgumentNull("func"); if (resultSelector == null) throw Error.ArgumentNull("resultSelector"); TAccumulate result = seed; foreach (TSource element in source) { result = func(result, element); } return resultSelector(result); }

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C# LINQ Aggregation Methods

Aggregate (LINQ)

Aggregate alternative for Sum

Aggregate alternative for Average

Aggregate Implementation

See also