ParallelEnumerable::ToLookup<TSource, TKey> Method (ParallelQuery<TSource>, Func<TSource, TKey>, IEqualityComparer<TKey>)
Creates an ILookup<TKey, TElement> from a ParallelQuery<TSource> according to a specified key selector function and key comparer.
Assembly: System.Core (in System.Core.dll)
[ExtensionAttribute] public: generic<typename TSource, typename TKey> static ILookup<TKey, TSource>^ ToLookup( ParallelQuery<TSource>^ source, Func<TSource, TKey>^ keySelector, IEqualityComparer<TKey>^ comparer )
Type Parameters
- TSource
The type of elements of source.
- TKey
The type of the key returned by keySelector.
Parameters
- source
- Type: System.Linq::ParallelQuery<TSource>
The sequence to create a ILookup<TKey, TElement> from.
- keySelector
- Type: System::Func<TSource, TKey>
A function to extract a key from each element.
- comparer
- Type: System.Collections.Generic::IEqualityComparer<TKey>
An IEqualityComparer<T> to compare keys.
Return Value
Type: System.Linq::ILookup<TKey, TSource>A ILookup<TKey, TElement> that contains keys and values.
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 keySelector or 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.
