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

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 Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Linq.IQueryable<TSource>
A sequence to aggregate over.
func
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.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable<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.

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 and LongCount, and four numeric aggregation methods, namely Max, Min, 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 =
                words.AsQueryable().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, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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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