The max operator emits the item of the source observable that contains the maximum value of the whole sequence. The following figure shows the marble diagram of this operator:

Its prototype is the following:

Observable.max(self, comparer=None)

Here, the comparer parameter is a function being used to compare items. If no comparer is provided, then the equality operator is used.

Here is an example of the max operator:

numbers = Observable.from_([1, 2, 3, 4])

numbers.max().subscribe(
    on_next = lambda i: print("on_next {}".format(i)),
    on_error = lambda e: print("on_error: {}".format(e)),
    on_completed = lambda: print("on_completed")
)

This example gives the following result:

on_next 4
on_completed