On Monday, September 5, 2016 at 10:42:27 AM UTC+1, Peter Otten wrote: > Antoon Pardon wrote: > > > I need an interator that takes an already existing iterator and > > divides it into subiterators of items belonging together. > > > > For instance take the following class, wich would check whether > > the argument is greater or equal to the previous argument. > > > > class upchecker: > > def __init__(self): > > self.prev = None > > def __call__(self, arg): > > if self.last is None: > > self.prev = arg > > return True > > elif arg >= self.last: > > self.prev = arg > > return True > > else: > > self.prev = arg > > return False > > > > So the iterator I need --- I call it grouped --- in combination with > > the above class would be used someting like: > > > > for itr in grouped([8, 10, 13, 11, 2, 17, 5, 12, 7, 14, 4, 6, 15, 16, 19, > > 9, 0, 1, 3, 18], upchecker()): > > print list(itr) > > > > and the result would be: > > > > [8, 10, 13] > > [11] > > [2, 17] > > [5, 12] > > [7, 14] > > [4, 6, 15, 16, 19] > > [9] > > [0, 1, 3, 18] > > > > Anyone an idea how I best tackle this? > > I always start thinking "There must be an elegant way to do this" and then > end with a clumsy wrapper around itertools.groupby(). > > $ cat grouped.py > from itertools import groupby > > > class Check: > def __init__(self, check): > self.first = True > self.prev = None > self.toggle = False > self.check = check > > def __call__(self, item): > if self.first: > self.first = False > else: > if not self.check(self.prev, item): > self.toggle = not self.toggle > self.prev = item > return self.toggle > > > def grouped(items, check): > return (g for k, g in groupby(items, Check(check))) > > > if __name__ == "__main__": > def upchecker(a, b): > return a < b > > items = [ > 8, 10, 13, 11, 2, 17, 5, 12, 7, 14, 4, 6, 15, 16, 19, 9, 0, 1, 3, 18 > ] > for itr in grouped(items, upchecker): > print(list(itr)) > > $ python grouped.py > [8, 10, 13] > [11] > [2, 17] > [5, 12] > [7, 14] > [4, 6, 15, 16, 19] > [9] > [0, 1, 3, 18]
As usual you beat me to it, but I'd spell "upchecker" as "from operator import lt" :) -- https://mail.python.org/mailman/listinfo/python-list
