Queryable.Average(Of TSource) Method (IQueryable(Of TSource), Expression(Of Func(Of TSource, Decimal)))

'Declaration
<ExtensionAttribute> _
Public Shared Function Average(Of TSource) ( _
	source As IQueryable(Of TSource), _
	selector As Expression(Of Func(Of TSource, Decimal)) _
) As Decimal

Usage Note

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 Average(Of TSource)(IQueryable(Of TSource), Expression(Of Func(Of TSource, Decimal))) method generates a MethodCallExpression that represents calling Average(Of TSource)(IQueryable(Of TSource), Expression(Of Func(Of TSource, Decimal))) 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 Average(Of TSource)(IQueryable(Of TSource), Expression(Of Func(Of TSource, Decimal))) depends on the implementation of the type of the source parameter. The expected behavior is that it calculates the average of the values in source after invoking selector on each value.

The following code example demonstrates how to use Average(Of TSource)(IQueryable(Of TSource), Expression(Of Func(Of TSource, Int32))) to calculate the average String length in a sequence of values of type String.

Note
This code example uses an overload of this overloaded method that is different from the specific overload that this topic describes. To extend the example to this topic, change the body of the selector function.

Dim fruits() As String = {"apple", "banana", "mango", "orange", "passionfruit", "grape"}

        ' Determine the average string length in the array. 
        Dim average As Double = fruits.AsQueryable().Average(Function(s) s.Length)

        MsgBox(String.Format("The average string length is {0}.", average))

        ' This code produces the following output: 
        ' 
        ' The average string length is 6.5. 

.NET Framework

.NET Framework Client Profile

Portable Class Library

.NET for Windows Store apps

Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Reference