ParallelEnumerable.GroupBy<TSource, TKey, TElement, TResult> Method (ParallelQuery<TSource>, Func<TSource, TKey>, Func<TSource, TElement>, Func<TKey, IEnumerable<TElement>, TResult>)
Groups in parallel the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. The elements of each group are projected by using a specified function.
Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
public static ParallelQuery<TResult> GroupBy<TSource, TKey, TElement, TResult>( this ParallelQuery<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector, Func<TKey, IEnumerable<TElement>, TResult> resultSelector )
Type Parameters
- TSource
The type of the elements of source.
- TKey
The type of the key returned by keySelector.
- TElement
The type of the elements in each IGrouping{TKey, TElement}.
- TResult
The type of the result value returned by resultSelector.
Parameters
- source
- Type: System.Linq.ParallelQuery<TSource>
A sequence whose elements to group.
- keySelector
- Type: System.Func<TSource, TKey>
A function to extract the key for each element.
- elementSelector
- Type: System.Func<TSource, TElement>
A function to map each source element to an element in an IGrouping<TKey, TElement>.
- resultSelector
- Type: System.Func<TKey, IEnumerable<TElement>, TResult>
A function to create a result value from each group.
Return Value
Type: System.Linq.ParallelQuery<TResult>A sequence of elements of type TResult 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 ParallelQuery<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 |
|---|---|
| OperationCanceledException | The query was canceled with the token passed in through WithCancellation. |
| ArgumentNullException | source or action is a null reference (Nothing in Visual Basic). |
| AggregateException | One or more exceptions occurred during the evaluation of the query. |
Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
