Synchronize events in rx in simulations

Question

I have the following streams

T1---T2---T3---T4---T5---T6---T7---T8
Q1-Q3-Q7-Q10

I would like to combine them so it looks like this

Q1--------Q3------------------Q7-----

i,e, only release the event Qi when Ti is released.

Is there a simple way to achieve this using RX primitive?

Answer 1

If your relationship is oneway only (that is T event occurs before matching Q one), you can achieve this with (js syntax to be confirmed):

tElts.selectMany(i -> qElts.takeWhile(n -> n<=i).where(n -> n==i))

The inner stream will return a single element stream Q3 for T3, and an empty stream for T2.

Answer 2

I am not sure if you are looking for a JavaScript solution or something in the System.Reactive namespace. I have this .NET solution that works. This solution assumes that the Q's will always be generated faster than the T's, i.e. Q_n will never be generated after T_n for all n.

// Generate 8 T's, 1 per second.
IObservable<int> tSource = 
    Observable
    .Interval(TimeSpan.FromSeconds(1))
    .Select(x => (int)(x + 1))
    .Take(8);

// Generate 4 Q's immediately.
IObservable<int> qSource =
    (new int[] { 1, 3, 7, 10 })
    .ToObservable();

var result = 
    qSource
    .SelectMany(x => 
        tSource
        .Where(y => x == y)
        .Take(1));

Interesting note, this looks like the dual of Gluck's solution which also works.

Answer 3

The zip operator synchronizes multiple streams.