Queryable.Aggregate(Of TSource) Method (IQueryable(Of TSource), Expression(Of Func(Of TSource, TSource, TSource)))
Applies an accumulator function over a sequence.
Assemblies: System.Linq.Queryable (in System.Linq.Queryable.dll)
System.Core (in System.Core.dll)
'Declaration <ExtensionAttribute> _ Public Shared Function Aggregate(Of TSource) ( _ source As IQueryable(Of TSource), _ func As Expression(Of Func(Of TSource, TSource, TSource)) _ ) As TSource
The type of the elements of source.
- Type: System.Linq.IQueryable(Of )
A sequence to aggregate over.
The final accumulator value.
Usage NoteIn Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable(Of ). 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).
This method has at least one parameter of type Expression(Of TDelegate) whose type argument is one of the Func(Of T, TResult) types. For these parameters, you can pass in a lambda expression and it will be compiled to an Expression(Of TDelegate).
The method generates a MethodCallExpression that represents calling itself as a constructed generic method. It then passes the MethodCallExpression to the Execute(Of 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 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 to build a sentence from an array of strings.
Dim sentence As String = "the quick brown fox jumps over the lazy dog" ' Split the string into individual words. Dim words() As String = sentence.Split(" "c) ' Use Aggregate() to prepend each word to the beginning of the ' new sentence to reverse the word order. Dim reversed As String = _ words.AsQueryable().Aggregate( _ Function(ByVal workingSentence, ByVal nextWord) nextWord & " " & workingSentence _ ) MsgBox(reversed) ' This code produces the following output: ' ' dog lazy the over jumps fox brown quick the