Between values with Rx

Question

Is there some extension method in Rx to do the scenario below?

I have a value to start the pumping (green circles) and other value to stop the pumping (reed circles), the blue circles should be the expected values, I would not want this command to be canceled and recreated (ie "TakeUntil" and "SkipUntil" will not work).

The implementation using LINQ would be something like this:

  public static IEnumerable<T> TakeBetween<T>(this IEnumerable<T> source, Func<T, bool> entry, Func<T, bool> exit)
    {
        bool yield = false;
        foreach (var item in source)
        {
            if (!yield)
            {
                if (!entry(item)) 
                    continue;

                yield = true;
                continue;
            }

            if (exit(item))
            {
                yield = false;
                continue;
            }

            yield return item;
        }
    }

How could this same logic for IObservable<T> ?

Answer 1

Here's what you need as an extension method:

public static IObservable<T> TakeBetween<T>(
    this IObservable<T> source,
    Func<T, bool> entry,
    Func<T, bool> exit)
{
    return source
        .Publish(xs =>
        {
            var entries = xs.Where(entry);
            var exits = xs.Where(exit);
            return xs.Window(entries, x => exits);
        })
        .Switch();
}

The key thing I've included in this is the used of the Publish extension. In this particular case it is important as your source observable may be "hot" and this enables the source values to be shared without creating multiple subscriptions to the source.

Answer 2

I think you can use Window:

source.Window(entrySignal, _ => exitSignal).Switch();