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Queryable.Aggregate<TSource> Method (IQueryable<TSource>, Expression<Func<TSource, TSource, TSource>>)


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Applies an accumulator function over a sequence.

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

public static TSource Aggregate<TSource>(
	this IQueryable<TSource> source,
	Expression<Func<TSource, TSource, TSource>> func


Type: System.Linq.IQueryable<TSource>

A sequence to aggregate over.

Type: System.Linq.Expressions.Expression<Func<TSource, TSource, TSource>>

An accumulator function to apply to each element.

Return Value

Type: TSource

The final accumulator value.

Type Parameters


The type of the elements of source.

Exception Condition

source or func is null.


source contains no elements.

This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T, TResult> types. For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

The Aggregate<TSource>(IQueryable<TSource>, Expression<Func<TSource, TSource, TSource>>) method generates a MethodCallExpression that represents calling Aggregate<TSource>(IQueryable<TSource>, Expression<Func<TSource, TSource, TSource>>) itself as a constructed generic method. It then passes the MethodCallExpression to the Execute<TResult>(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

The query behavior that occurs as a result of executing an expression tree that represents calling Aggregate<TSource>(IQueryable<TSource>, Expression<Func<TSource, TSource, TSource>>) depends on the implementation of the type of the source parameter. The expected behavior is that the specified function, func, is applied to each value in the source sequence and the accumulated value is returned. The first value in source is used as the seed value for the accumulated value, which corresponds to the first parameter in func.

To simplify common aggregation operations, the set of standard query operators also includes two counting methods, Count<TSource> and LongCount<TSource>, and four numeric aggregation methods, namely Max<TSource>, Min<TSource>, Sum, and Average.

The following code example demonstrates how to use Aggregate<TSource>(IQueryable<TSource>, Expression<Func<TSource, TSource, TSource>>) 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(' ');

// Use Aggregate() to prepend each word to the beginning of the 
// new sentence to reverse the word order.
string reversed =
    (workingSentence, next) => next + " " + workingSentence


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

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.1
Windows Phone
Available since 8.1
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