Queryable.GroupBy<'TSource, 'TKey> Method (IQueryable<'TSource>, Expression<Func<'TSource, 'TKey>>)
Groups the elements of a sequence according to a specified key selector function.
Assembly: System.Core (in System.Core.dll)
static member GroupBy<'TSource, 'TKey> : source:IQueryable<'TSource> * keySelector:Expression<Func<'TSource, 'TKey>> -> IQueryable<IGrouping<'TKey, 'TSource>>
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.
Return Value
Type: System.Linq.IQueryable<IGrouping<'TKey, 'TSource>>An IQueryable<IGrouping<TKey, TSource>> in C# or IQueryable(Of IGrouping(Of TKey, TSource)) in Visual Basic where each IGrouping<'TKey, 'TElement> object contains a sequence of objects and a key.
Type Parameters
- TSource
The type of the elements of source.
- TKey
The type of the key returned by the function represented in keySelector.
| Exception | Condition |
|---|---|
| ArgumentNullException | source or keySelector 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>(IQueryable<'TSource>, Expression<Func<'TSource, 'TKey>>) method generates a MethodCallExpression that represents calling GroupBy<'TSource, 'TKey>(IQueryable<'TSource>, Expression<Func<'TSource, 'TKey>>) 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>(IQueryable<'TSource>, Expression<Func<'TSource, 'TKey>>) 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.
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.1
Windows Phone
Available since 8.1