Here's my version, which has one loop for increasing sequences, and another loop for decreasing sequences. I think that makes it easier to understand what's go

Here's my version, which has one loop for increasing sequences, and another loop for decreasing sequences. I think that makes it easier to understand what's going on. It properly handles runs of equal elements, and it handles neither-greater-nor-lesser values like NaN in a relatively principled fashion: putting them in a run by themselves. Perhaps this code is over-commented. from more_itertools import peekable def mono_runs(seq): it = peekable(iter(seq)) while it: # While any elements left... # Consume the first element. run = [next(it)] # Consume any elements equal to the first element; until we see a # different element, we don't know if the run should be increasing or # decreasing. while it and it.peek() == run[-1]: run.append(next(it)) # Consume the rest of the run. if it and it.peek() > run[-1]: # Next is a higher element; this is an increasing sequence. while it and it.peek() >= run[-1]: run.append(next(it)) elif it and it.peek() < run[-1]: # Next is a lower element; this is a decreasing sequence. while it and it.peek() <= run[-1]: run.append(next(it)) run.reverse() # Else, either we're out of elements, or the next element is neither # higher nor lower (e.g. NaN). Either way, the run ends here. yield run