Average Method (IEnumerable(Nullable(Double)))

# Enumerable.Average Method (IEnumerable<Nullable<Double>>)

Computes the average of a sequence of nullable Double values.

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

## Syntax

```public static Nullable<double> Average(
this IEnumerable<Nullable<double>> source
)
```

#### Parameters

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

#### Return Value

Type: System.Nullable<Double>
The average of the sequence of values, or null if the source sequence is empty or contains only values that are null.

#### Usage Note

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

## Exceptions

ExceptionCondition
ArgumentNullException

source is null.

## Remarks

If the sum of the elements is too large to represent as a Double, this method returns positive or negative infinity.

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

## Examples

The following code example demonstrates how to use Average(IEnumerable<Nullable<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, substitute the elements of the source sequence with elements of the appropriate numerical type.

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

double? average = longs.Average();

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

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

```

## Version Information

#### Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone