How do I keep count of Hot observables?

Question

I have the following Observable.

IObservable<MyDto> observable;

Now in order to count the number of items in Observable I cannot use the following code because my observable is Hot and long running and subscription to the 'count' will never be called.

var count = observable.Count()

I am looking to get the count every time an item arrives, here is something I am trying to do

observable.Subscribe(o => Console.WriteLine(" Object received "));
observable.Count().Subscribe(c => Console.WriteLine("Current count is " + c.ToString() + " but this is not final count, more are coming"));

How can I achieve this?

Answer 1

Use Scan:

observable
    .Scan(0, (count, _) => count + 1)
    .Subscribe(count => Console.WriteLine("Current count is " + count));