RX: How to process n buffered items from a sequence then wait t seconds before processing the next n items?

Question

I'm trying to figure out how to process n buffered items from a sequence then wait t seconds before processing the next n items?

Here's a crude form of what I'm trying to do, using Thread.Sleep(). I want to avoid Thread.Sleep() and do it properly.

static void Main(string[] args)
{
    var t = Observable.Range(0, 100000);

    var query = t.Buffer(20);                       

    query.ObserveOn(NewThreadScheduler.Default)
        .Subscribe(x => DoStuff(x));

    Console.WriteLine("Press ENTER to exit");
    Console.ReadLine();

}

static void DoStuff(IList<int> list)
{
    Console.WriteLine(DateTime.Now);

    foreach (var value in list)
    {
        Console.WriteLine(value);
    }

    Thread.Sleep(TimeSpan.FromSeconds(10));
}

Can any one help me find a more RX way of doing this?

Thanks

Flash

Answer 1

// Instantiate this once, we'll use it in a closure multiple times.
var delay = Observable.Empty<int>().Delay(TimeSpan.FromMilliseconds(10));

// start with a source of individual items to be worked.
Observable.Range(0, 100000)
    // Create batches of work.
    .Buffer(20)
    // Select an observable for the batch of work, and concat a delay.
    .Select(batch => batch.ToObservable().Concat(delay))
    // Concat those together and form a "process, delay, repeat" observable.
    .Concat()
    // Subscribe!
    .Subscribe(Console.WriteLine);

// Make sure we wait for our work to be done.
// There are other ways to sync up, like async / await.
Console.ReadLine();

Alternatively, you could also sync up using async/await:

static IObservable<int> delay = Observable.Empty<int>().Delay(TimeSpan.FromMilliseconds(100));

static async Task Run()
{
    await Observable.Range(0, 1000)
        .Buffer(20)
        .Select(batch => batch.ToObservable().Concat(delay))
        .Concat()
        .Do(Console.WriteLine)
        .LastOrDefaultAsync();
}

Isn't that delay observable a nifty trick? It works because OnCompleted is delayed just like OnNext!

Answer 2

Building on Christopher's answer if you don't want the list elements flattened out you could do:

var delay = Observable.Empty<IList<int>>().Delay(TimeSpan.FromSeconds(10));

var query = Observable.Range(0, 100000)
                      .Buffer(20)
                      .Select(batch => Observable.Return(batch).Concat(delay))
                      .Concat();

query.Subscribe(list =>
                    {
                        Console.WriteLine(DateTime.Now);

                        foreach (var value in list)
                        {
                            Console.WriteLine(value);
                        }
                    });