项目
11/18/2011

Queryable.Average Method (IQueryable<Nullable<Int32>>)

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Computes the average of a sequence of nullable Int32 values.

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

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function Average ( _
    source As IQueryable(Of Nullable(Of Integer)) _
) As Nullable(Of Double)

public static Nullable<double> Average(
    this IQueryable<Nullable<int>> source
)

Parameters

source
Type: System.Linq.IQueryable<Nullable<Int32>>
A sequence of nullable Int32values to calculate the average of.

Return Value

Type: System.Nullable<Double>
The average of the sequence of values, or nulla null reference (Nothing in Visual Basic) if the source sequence is empty or contains only nulla null reference (Nothing in Visual Basic) values.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable<Nullable<Int32>>. When you use instance method syntax to call this method, omit the first parameter.

Exceptions

Exception	Condition
ArgumentNullException	source is nulla null reference (Nothing in Visual Basic).

Remarks

The Average(IQueryable<Nullable<Int32>>) method generates a MethodCallExpression that represents calling Average(IQueryable<Nullable<Int32>>) itself. 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 Average(IQueryable<Nullable<Int32>>) 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.

Examples

The following code example demonstrates how to use Average(IQueryable<Nullable<Int64>>) to calculate the average of a sequence of values.

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, substitute the elements of the source sequence with elements of the appropriate numerical type.

      Dim longs() As Nullable(Of Long) = {Nothing, 10007L, 37L, 399846234235L}

      Dim average As Nullable(Of Double) = longs.AsQueryable().Average()

      outputBlock.Text &= String.Format("The average is {0}.", average) & vbCrLf

      ' This code produces the following output:
      '
      ' The average is 133282081426.333.

         long?[] longs = { null, 10007L, 37L, 399846234235L };

         double? average = longs.AsQueryable().Average();

         outputBlock.Text += String.Format("The average is {0}.", average) + "\n";

         // This code produces the following output:
         //
         // The average is 133282081426.333.

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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