ParallelEnumerable.ToLookup(Of TSource, TKey, TElement) Method (ParallelQuery(Of TSource), Func(Of TSource, TKey), Func(Of TSource, TElement), IEqualityComparer(Of TKey))
Creates an ILookup(Of TKey, TElement) from a ParallelQuery(Of TSource) according to a specified key selector function, a comparer and an element selector function.
Assembly: System.Core (in System.Core.dll)
<ExtensionAttribute> Public Shared Function ToLookup(Of TSource, TKey, TElement) ( source As ParallelQuery(Of TSource), keySelector As Func(Of TSource, TKey), elementSelector As Func(Of TSource, TElement), comparer As IEqualityComparer(Of TKey) ) As ILookup(Of TKey, TElement)
Parameters
- source
-
Type:
System.Linq.ParallelQuery(Of TSource)
The sequence to create a ILookup(Of TKey, TElement) from.
- keySelector
-
Type:
System.Func(Of TSource, TKey)
A function to extract a key from each element.
- elementSelector
-
Type:
System.Func(Of TSource, TElement)
A transform function to produce a result element value from each element.
- comparer
-
Type:
System.Collections.Generic.IEqualityComparer(Of TKey)
An IEqualityComparer(Of T) to compare keys.
Return Value
Type: System.Linq.ILookup(Of TKey, TElement)A Lookup<(Of <(TKey, TElement>)>) that contains values of type TElement selected from the input sequence.
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.
| 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. |
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone
Available since 8.1