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rxjsreactivexrx.net
wonderful world
wonderful world

Reputation: 11599

Equivalent of RxJS switchMap in ReactiveX/Rx.NET

In RxJS, there is a switchMap function. Is there an equivalent in ReactiveX/Rx.NET? I don't see one in the transforming documentation.

Upvotes: 10

Views: 4240

Answers (4)

Eduardo Brites
Eduardo Brites

Reputation: 4776

I created some C# extensions similar to the switchMap, concatMap and mergeMap:

public static class ReactiveExtensions
{
    public static IObservable<TOutput> SwitchSelect<TInput, TOutput>(this IObservable<TInput> source, Func<TInput, IObservable<TOutput>> selector) => source
        .Select(selector)
        .Switch();

    public static IObservable<TOutput> ConcatSelect<TInput, TOutput>(this IObservable<TInput> source, Func<TInput, IObservable<TOutput>> selector) => source
         .Select(selector)
         .Concat();

    public static IObservable<TOutput> MergeSelect<TInput, TOutput>(this IObservable<TInput> source, Func<TInput, IObservable<TOutput>> selector) => source
        .Select(selector)
        .Merge();
}

Then you can use it like:

Observable
   .Timer(someTimer)
   .SwitchSelect(_ => Observable.FromAsync(() => foo.RunAsyncMethod()))
   .Subscribe();

Upvotes: 0

Tyler Jennings
Tyler Jennings

Reputation: 8911

Edit

switch is the equivalent. http://reactivex.io/documentation/operators/switch.html

In short, switchMap and switch will cancel any previous streams whereas flatMap will not.

Upvotes: -4

vimant
vimant

Reputation: 21

From http://reactivex.io/documentation/operators/switch.html

Switch operator subscribes to an Observable that emits Observables. Each time it observes one of these emitted Observables, the Observable returned by Switch unsubscribes from the previously-emitted Observable begins emitting items from the latest Observable.

As MorleyDev pointed, the .NET implementation is https://learn.microsoft.com/en-us/previous-versions/dotnet/reactive-extensions/hh229197(v=vs.103), so the equivalent of RxJS switchMap in Rx.NET is a combination of Switch and Select operators:

// RxJS
observableOfObservables.pipe(
    switchMap(next => transform(next))
    ...
)

// RX.Net
observableOfObservables
    .Switch()
    .Select(next => transform(next))
    ...

Upvotes: 2

MorleyDev
MorleyDev

Reputation: 141

There is no single SwitchMany in Rx.NET equivalent to switchMap in Rx.js. You need to use separate Select and Switch functions.

Observable.Interval(TimeSpan.FromMinutes(1))
    .Select(_ => Observable.Return(10))
    .Switch()

Documentation: https://msdn.microsoft.com/en-us/library/hh229197(v=vs.103).aspx

Upvotes: 14

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