Observable.ToLookup<TSource, TKey, TElement> Method (IObservable<TSource>, Func<TSource, TKey>, Func<TSource, TElement>)

Creates a lookup from an observable sequence according to a specified key selector function, and an element selector function.

Namespace:  System.Reactive.Linq
Assembly:  System.Reactive (in System.Reactive.dll)

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function ToLookup(Of TSource, TKey, TElement) ( _
    source As IObservable(Of TSource), _
    keySelector As Func(Of TSource, TKey), _
    elementSelector As Func(Of TSource, TElement) _
) As IObservable(Of ILookup(Of TKey, TElement))
'Usage
Dim source As IObservable(Of TSource)
Dim keySelector As Func(Of TSource, TKey)
Dim elementSelector As Func(Of TSource, TElement)
Dim returnValue As IObservable(Of ILookup(Of TKey, TElement))

returnValue = source.ToLookup(keySelector, _
    elementSelector)

Type Parameters

  • TSource
    The type of source.
  • TKey
    The type of key.
  • TElement
    The type of element.

Parameters

  • 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.

Return Value

Type: System.IObservable<ILookup<TKey, TElement>>
A lookup from an observable sequence according to a specified key selector function, and an element selector function.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IObservable<TSource>. When you use instance method syntax to call this method, omit the first parameter. For more information, see or .

See Also

Reference

Observable Class

ToLookup Overload

System.Reactive.Linq Namespace