Queryable::Average<TSource> Method (IQueryable<TSource>, Expression<Func<TSource, Nullable<Double>>>)
Computes the average of a sequence of nullable Double values that is obtained by invoking a projection function on each element of the input sequence.
Assembly: System.Core (in System.Core.dll)
[ExtensionAttribute] public: generic<typename TSource> static Nullable<double> Average( IQueryable<TSource>^ source, Expression<Func<TSource, Nullable<double>>^>^ selector )
The type of the elements of source.
- Type: System.Linq::IQueryable<>
A sequence of values to calculate the average of.
Return ValueType: System::Nullable<Double>
The average of the sequence of values, or nullptr if the source sequence is empty or contains only nullptr values.
Usage NoteIn Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable<>. 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).
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 method generates a MethodCallExpression that represents calling 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 depends on the implementation of the type of the source parameter. The expected behavior is that it calculates the average of the values in source after invoking selector on each value.
The following code example demonstrates how to use Average<TSource>(IQueryable<TSource>, Expression<Func<TSource, Int32>>) to calculate the average String length in a sequence of values of type String.
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.