Issue 13252: new decumulate() function in itertools module (original) (raw)

Created on 2011-10-23 22:32 by carlo.verre, last changed 2022-04-11 14:57 by admin. This issue is now closed.

Messages (4)
msg146263 - (view)	Author: Carlo Verre (carlo.verre)	Date: 2011-10-23 22:32
After in Python 3.2 the accumulate() function has been added to itertools module, for self-evident reasons of completeness and symmetry we could add in 3.3 the inverse decumulate() function, which, given the iterable argument p, yields p[0], p[1] - p[0], p[2] - p[1]... Its equivalent python form is in the attached file decumulate.py, below.
msg146290 - (view)	Author: Alyssa Coghlan (ncoghlan) *	Date: 2011-10-24 10:45
OK, looking at the code I realised what you're trying to get at is the idea of reporting the differences between values in a series, such that: x = list(accumulate(seq)) assert x == list(accumulate(differences(x))) I don't think the use cases are there to justify the addition (not every iterator we can think of should be a building block in itertools), but if such a thing were to be added, "differences" would convey the intention significantly better than the invented term "decumulate".
msg166167 - (view)	Author: Ezio Melotti (ezio.melotti) *	Date: 2012-07-22 20:29
I don't think this should go in itertools. It could go in the recipes at the bottom of the itertools doc, if you can provide some valid use cases (and possibly a patch too).
msg168260 - (view)	Author: Raymond Hettinger (rhettinger) *	Date: 2012-08-15 05:40
I also agree that the itertools module doesn't need this. (Reasons of "symmetry" are insufficient to make the module fatter that it already is). In addition, there are already a number of simple ways to do this.