ParallelEnumerable::GroupBy<TSource, TKey, TElement, TResult> Method (ParallelQuery<TSource>^, Func<TSource, TKey>^, Func<TSource, TElement>^, Func<TKey, IEnumerable<TElement>^, TResult>^, IEqualityComparer<TKey>^)
Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. Key values are compared by using a specified comparer, and the elements of each group are projected by using a specified function.
Assembly: System.Core (in System.Core.dll)
public: generic<typename TSource, typename TKey, typename TElement, typename TResult> [ExtensionAttribute] static ParallelQuery<TResult>^ GroupBy( ParallelQuery<TSource>^ source, Func<TSource, TKey>^ keySelector, Func<TSource, TElement>^ elementSelector, Func<TKey, IEnumerable<TElement>^, TResult>^ resultSelector, IEqualityComparer<TKey>^ comparer )
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{Key, TElement}.
- resultSelector
-
Type:
System::Func<TKey, IEnumerable<TElement>^, TResult>^
A function to create a result value from each group.
- comparer
-
Type:
System.Collections.Generic::IEqualityComparer<TKey>^
An IEqualityComparer<T> to compare keys.
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.
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.
| 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. |
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone
Available since 8.1