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

Computes the sum of the sequence of 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)
public static double Sum<TSource>(
	this IQueryable<TSource> source,
	Expression<Func<TSource, 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, Double>>

A projection function to apply to each element.

Return Value

Type: System.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. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).
ExceptionCondition
ArgumentNullException

source or selector is null.

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

The following code example demonstrates how to use Sum<TSource>(IQueryable<TSource>, Expression<Func<TSource, Double>>) to sum the projected values of a sequence.

NoteNote:

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.

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);

    Console.WriteLine("The total weight of the packages is: {0}", totalWeight);
}

/*
    This code produces the following output:

    The total weight of the packages is: 83.7
*/

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5
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