[SOLVED] Python – How to check list monotonicity

Issue

What would be an efficient and pythonic way to check list monotonicity?
i.e. that it has monotonically increasing or decreasing values?

Examples:

[0, 1, 2, 3, 3, 4]   # This is a monotonically increasing list
[4.3, 4.2, 4.2, -2]  # This is a monotonically decreasing list
[2, 3, 1]            # This is neither

Solution

It’s better to avoid ambiguous terms like “increasing” or “decreasing” as it’s not clear if equality is acceptable or not. You should always use either for example “non-increasing” (clearly equality is accepted) or “strictly decreasing” (clearly equality is NOT accepted).

def strictly_increasing(L):
    return all(x<y for x, y in zip(L, L[1:]))

def strictly_decreasing(L):
    return all(x>y for x, y in zip(L, L[1:]))

def non_increasing(L):
    return all(x>=y for x, y in zip(L, L[1:]))

def non_decreasing(L):
    return all(x<=y for x, y in zip(L, L[1:]))

def monotonic(L):
    return non_increasing(L) or non_decreasing(L)

Answered By – 6502

Answer Checked By – Mary Flores (BugsFixing Volunteer)

Leave a Reply

Your email address will not be published. Required fields are marked *