Queryable::GroupBy<TSource, TKey, TElement> Method (IQueryable<TSource>^, Expression<Func<TSource, TKey>^>^, Expression<Func<TSource, TElement>^>^)


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Groups the elements of a sequence according to a specified key selector function and projects the elements for each group by using a specified function.

Namespace:   System.Linq
Assembly:  System.Core (in System.Core.dll)

generic<typename TSource, typename TKey, typename TElement>
static IQueryable<IGrouping<TKey, TElement>^>^ GroupBy(
	IQueryable<TSource>^ source,
	Expression<Func<TSource, TKey>^>^ keySelector,
	Expression<Func<TSource, TElement>^>^ elementSelector


Type: System.Linq::IQueryable<TSource>^

An IQueryable<T> whose elements to group.

Type: System.Linq.Expressions::Expression<Func<TSource, TKey>^>^

A function to extract the key for each element.

Type: System.Linq.Expressions::Expression<Func<TSource, TElement>^>^

A function to map each source element to an element in an IGrouping<TKey, TElement>.

Return Value

Type: System.Linq::IQueryable<IGrouping<TKey, TElement>^>^

An IQueryable<IGrouping<TKey, TElement>> in C# or IQueryable(Of IGrouping(Of TKey, TElement)) in Visual Basic where each IGrouping<TKey, TElement> contains a sequence of objects of type TElement and a key.

Type Parameters


The type of the elements of source.


The type of the key returned by the function represented in keySelector.


The type of the elements in each IGrouping<TKey, TElement>.

Exception Condition

source or keySelector or elementSelector 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 GroupBy<TSource, TKey, TElement>(IQueryable<TSource>^, Expression<Func<TSource, TKey>^>^, Expression<Func<TSource, TElement>^>^) method generates a MethodCallExpression that represents calling GroupBy<TSource, TKey, TElement>(IQueryable<TSource>^, Expression<Func<TSource, TKey>^>^, Expression<Func<TSource, TElement>^>^) 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, TElement>(IQueryable<TSource>^, Expression<Func<TSource, TKey>^>^, Expression<Func<TSource, TElement>^>^) 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. It invokes elementSelector on each element to obtain a result element.

The following code example demonstrates how to use GroupBy<TSource, TKey, TElement>(IQueryable<TSource>^, Expression<Func<TSource, TKey>^>^, Expression<Func<TSource, TElement>^>^) to group the elements of a sequence.

No code example is currently available or this language may not be supported.

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.1
Windows Phone
Available since 8.1
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