Article
11/18/2011

Queryable.Sum<TSource> Method (IQueryable<TSource>, Expression<Func<TSource, Nullable<Double>>>)

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Computes the sum of the sequence of nullable Double values that is obtained by invoking a projection 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 IQueryable(Of TSource), _
    selector As Expression(Of Func(Of TSource, Nullable(Of Double))) _
) As Nullable(Of Double)

public static Nullable<double> Sum<TSource>(
    this IQueryable<TSource> source,
    Expression<Func<TSource, Nullable<double>>> selector
)

Type Parameters

TSource
The type of the elements of source.

Parameters

source
Type: System.Linq.IQueryable<TSource>
A sequence of values of type TSource.

selector
Type: System.Linq.Expressions.Expression<Func<TSource, Nullable<Double>>>
A projection function to apply to each element.

Return Value

Type: System.Nullable<Double>
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 IQueryable<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

This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T, TResult> types. For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

The Sum<TSource>(IQueryable<TSource>, Expression<Func<TSource, Nullable<Double>>>) method generates a MethodCallExpression that represents calling Sum<TSource>(IQueryable<TSource>, Expression<Func<TSource, Nullable<Double>>>) itself as a constructed generic method. 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 Sum<TSource>(IQueryable<TSource>, Expression<Func<TSource, Nullable<Double>>>) depends on the implementation of the type of the source parameter. The expected behavior is that it invokes selector on each element of source and returns the sum of the resulting values.

Examples

The following code example demonstrates how to use Sum<TSource>(IQueryable<TSource>, Expression<Func<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

   Shared Sub SumEx3()
      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}})

      ' Calculate the sum of all package weights.
      Dim totalWeight As Double = packages.AsQueryable().Sum(Function(pkg) pkg.Weight)

      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

         class Package
         {
            public string Company { get; set; }
            public double Weight { get; set; }
         }

         public static void SumEx3()
         {
            List<Package> packages =
                new List<Package> 
                        { new Package { Company = "Coho Vineyard", Weight = 25.2 },
                          new Package { Company = "Lucerne Publishing", Weight = 18.7 },
                          new Package { Company = "Wingtip Toys", Weight = 6.0 },
                          new Package { Company = "Adventure Works", Weight = 33.8 } };

            // Calculate the sum of all package weights.
            double totalWeight = packages.AsQueryable().Sum(pkg => pkg.Weight);

            outputBlock.Text += String.Format("The total weight of the packages is: {0}", totalWeight) + "\n";
         }

         /*
             This code produces the following output:

             The total weight of the packages is: 83.7
         */

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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