ParallelEnumerable.ToLookup<TSource, TKey, TElement> Method (ParallelQuery<TSource>, Func<TSource, TKey>, Func<TSource, TElement>, IEqualityComparer<TKey>)
Creates an ILookup<TKey, TElement> from a ParallelQuery<TSource> according to a specified key selector function, a comparer and an element selector function.
Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
public static ILookup<TKey, TElement> ToLookup<TSource, TKey, TElement>( this ParallelQuery<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector, IEqualityComparer<TKey> comparer )
Type Parameters
- TSource
The type of elements of source.
- TKey
The type of the key returned by keySelector.
- TElement
The type of the value returned by elementSelector.
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.
- elementSelector
- Type: System.Func<TSource, TElement>
A transform function to produce a result element value from each element.
- comparer
- Type: System.Collections.Generic.IEqualityComparer<TKey>
An IEqualityComparer<T> to compare keys.
Return Value
Type: System.Linq.ILookup<TKey, TElement>A Lookup<(Of <(TKey, TElement>)>) that contains values of type TElement selected from the input sequence.
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 elementSelector 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.
