How can you print something each time an item is emitted?

It is possible to implement a side-effect without changing the items emitted on an operator chain by using the do_action operator. This operator allows us to call a function on each event type received from its source observable.

How can you compute a value from all the items of an observable?

Two operators can be used to compute a value from all items emitted on an observable: the scan and the reduce operators. Both operators call a function for each item, with an accumulator as input (on top of the item itself). This function must return the updated value of the accumulator.

The difference between scan and reduce is that scan emits the value of the accumulator for each item, while reduce only emits the value when the source observable completes.

How can you subscribe to the latest observable emitted by a higher...