Find monotonic sequences in a list?

Question

I\'m new in Python but basically I want to create sub-groups of element from the list with a double loop, therefore I gonna compare the first element with the next to figure

Answer 1

@uselpa's version is fine. Here's mine (same issue with [50] instead of just 50) that uses collections.deque to be a little more efficient, and also some long comments...

#! /usr/bin/env python

from collections import deque

def process(lst):
    """
    Given a list of values that is not sorted (such that for some
    valid indices i,j, i lst[j]), produce a
    new list-of-lists, such that in the new list, each sublist *is*
    sorted:
        for all sublist \elem returnval:
            assert_is_sorted(sublist)
    and furthermore this is the minimal set of sublists required
    to achieve the condition.

    Thus, if the input list lst is actually sorted, this returns
    [list(lst)].
    """
    def sublist(deq):
        """
        Pop items off the front of deque deq until the next one
        goes backwards.  Return the constructed sub-list.
        """
        sub = [deq.popleft()]
        while deq and deq[0] >= sub[-1]:
            sub.append(deq.popleft())
        return sub

    # Make a copy of lst before modifying it; use a deque so that
    # we can pull entries off it cheaply.
    deq = deque(lst)
    output = []
    ret = []
    while deq:
        ret.append(sublist(deq))
    return ret

print process([45,78,120,47,58,50,32,34])

(Incidentally, in the days before collections.deque I'd probably just use a reversed copy of lst and use lst.pop() in sublist. That's not quite as obvious, though.)