Queryable::GroupBy<TSource, TKey, TResult> Method (IQueryable<TSource>, Expression<Func<TSource, TKey>>, Expression<Func<TKey, IEnumerable<TSource>, TResult>>)
Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key.
Assembly: System.Core (in System.Core.dll)
[ExtensionAttribute] public: generic<typename TSource, typename TKey, typename TResult> static IQueryable<TResult>^ GroupBy( IQueryable<TSource>^ source, Expression<Func<TSource, TKey>^>^ keySelector, Expression<Func<TKey, IEnumerable<TSource>^, TResult>^>^ resultSelector )
Type Parameters
- TSource
The type of the elements of source.
- TKey
The type of the key returned by the function represented in keySelector.
- TResult
The type of the result value returned by resultSelector.
Parameters
- source
- Type: System.Linq::IQueryable<TSource>
An IQueryable<T> whose elements to group.
- keySelector
- Type: System.Linq.Expressions::Expression<Func<TSource, TKey>>
A function to extract the key for each element.
- resultSelector
- Type: System.Linq.Expressions::Expression<Func<TKey, IEnumerable<TSource>, TResult>>
A function to create a result value from each group.
Return Value
Type: System.Linq::IQueryable<TResult>An T:System.Linq.IQueryable`1 that has a type argument of TResult and where each element represents a projection over a group and its key.
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).| Exception | Condition |
|---|---|
| ArgumentNullException | source or keySelector or resultSelector is nullptr. |
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 GroupBy<TSource, TKey, TResult>(IQueryable<TSource>, Expression<Func<TSource, TKey>>, Expression<Func<TKey, IEnumerable<TSource>, TResult>>) method generates a MethodCallExpression that represents calling GroupBy<TSource, TKey, TResult>(IQueryable<TSource>, Expression<Func<TSource, TKey>>, Expression<Func<TKey, IEnumerable<TSource>, TResult>>) itself as a constructed generic method. It then passes the MethodCallExpression to the CreateQuery<TElement>(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 GroupBy<TSource, TKey, TResult>(IQueryable<TSource>, Expression<Func<TSource, TKey>>, Expression<Func<TKey, IEnumerable<TSource>, TResult>>) depends on the implementation of the type of the source parameter. The expected behavior is that it groups the elements of source by a key value that is obtained by invoking keySelector on each element. The resultSelector parameter is used to obtain a result value from each group and its key.
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.