Статья
11/18/2011

Enumerable.Average<TSource> Method (IEnumerable<TSource>, Func<TSource, Nullable<Double>>)

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Computes the average of a sequence of nullable Double values that are obtained by invoking a transform function on each element of the input sequence.

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

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function Average(Of TSource) ( _
    source As IEnumerable(Of TSource), _
    selector As Func(Of TSource, Nullable(Of Double)) _
) As Nullable(Of Double)

public static Nullable<double> Average<TSource>(
    this IEnumerable<TSource> source,
    Func<TSource, Nullable<double>> selector
)

Type Parameters

TSource
The type of the elements of source.

Parameters

source
Type: System.Collections.Generic.IEnumerable<TSource>
A sequence of values to calculate the average of.

selector
Type: System.Func<TSource, Nullable<Double>>
A transform function to apply to each element.

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 values that are nulla null reference (Nothing in Visual Basic).

Usage Note

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

Exceptions

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

Remarks

In Visual Basic query expression syntax, an Aggregate Into Average() clause translates to an invocation of Average.

Examples

The following code example demonstrates how to use Average<TSource>(IEnumerable<TSource>, Func<TSource, Int64>) to calculate an average.

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.

      ' Create an array of strings.
      Dim numbers() As String = {"10007", "37", "299846234235"}

      ' Determine the average number after converting each
      ' string to an Int64 value.
      Dim avg As Double = _
          numbers.Average(Function(number) Convert.ToInt64(number))

      ' Display the output.
      outputBlock.Text &= "The average is " & avg & vbCrLf

      ' This code produces the following output:
      '
      ' The average is 99948748093

      string[] numbers = { "10007", "37", "299846234235" };

      double average = numbers.Average(num => Convert.ToInt64(num));

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

      // This code produces the following output:
      //
      // The average is 99948748093.

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

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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