Sum(TSource) Method (IEnumerable(TSource), Func(TSource, Nullable(Int32)))

# Enumerable.Sum(Of TSource) Method (IEnumerable(Of TSource), Func(Of TSource, Nullable(Of Int32)))

[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]

Computes the sum of the sequence of nullable Int32 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 Sum(Of TSource) ( _
source As IEnumerable(Of TSource), _
selector As Func(Of TSource, Nullable(Of Integer)) _
) As Nullable(Of Integer)
```

#### Type Parameters

TSource

The type of the elements of source.

#### Parameters

source
Type: System.Collections.Generic.IEnumerable(Of TSource)
A sequence of values that are used to calculate a sum.
selector
Type: System.Func(Of TSource, Nullable(Of Int32))
A transform function to apply to each element.

#### Return Value

Type: System.Nullable(Of Int32)
The sum of the projected values.

#### Usage Note

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

## Exceptions

ExceptionCondition
ArgumentNullException

source or selector is Nothing.

OverflowException

The sum is larger than MaxValue.

## Remarks

This method returns zero if source contains no elements.

The result does not include values that are Nothing.

You can apply this method to a sequence of arbitrary values if you provide a function, selector, that projects the members of source into a numeric type, specifically Nullable<Int32> in C# or Nullable(Of Int32) in Visual Basic.

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

## Examples

The following code example demonstrates how to use Sum(Of TSource)(IEnumerable(Of TSource), Func(Of TSource, Double)) to sum the projected values of a sequence.

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.

```
Structure Package
Public Company As String
Public Weight As Double
End Structure

Sub SumEx1()
' Create a list of Package values.
Dim packages As New List(Of Package)(New Package() _
{New Package With {.Company = "Coho Vineyard", .Weight = 25.2}, _
New Package With {.Company = "Lucerne Publishing", .Weight = 18.7}, _
New Package With {.Company = "Wingtip Toys", .Weight = 6.0}, _
New Package With {.Company = "Adventure Works", .Weight = 33.8}})

' Sum the values from each item's Weight property.
Dim totalWeight As Double = packages.Sum(Function(pkg) _
pkg.Weight)

' Display the result.
outputBlock.Text &= "The total weight of the packages is: " & totalWeight & VbCrLf
End Sub

' This code produces the following output:
'
' The total weight of the packages is: 83.7

```

## Version Information

#### Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone