sort dates in python array

Question

How to sort the below array of dates on python 2.4

 timestamps = ['2011-06-2', '2011-08-05', '2011-02-04', '2010-1-14', '2010-12-13', '2010-1-12', '2010-2-11', '2010-2-07', '2010-12-02', '2011-11-30', '2010-11-26', '2010-11-23', '2010-11-22', '2010-11-16']

Why are you using Python 2.4? – Tim Pietzcker Mar 02 '11 at 11:34 — Tim Pietzcker, Mar 02 '11 at 11:34

Tim Pietzcker · Answer 1 · 2017-01-10T10:09:28.673

66

>>> import datetime
>>> dates = [datetime.datetime.strptime(ts, "%Y-%m-%d") for ts in timestamps]
>>> dates.sort()
>>> sorteddates = [datetime.datetime.strftime(ts, "%Y-%m-%d") for ts in dates]
>>> sorteddates
['2010-01-12', '2010-01-14', '2010-02-07', '2010-02-11', '2010-11-16', '2010-11-
22', '2010-11-23', '2010-11-26', '2010-12-02', '2010-12-13', '2011-02-04', '2011
-06-02', '2011-08-05', '2011-11-30']

edited Jan 10 '17 at 10:09

answered Mar 02 '11 at 11:33

Tim Pietzcker

313,408
56
485
544

2

This is the most pythonic way I think. It scales to different formats of time, unlike the accepted answer. – CornSmith Sep 18 '13 at 18:21
3

best answer (+1) but you probably should not call the last object `sorted` as it is also the name of a [function](https://docs.python.org/2/library/functions.html#sorted) – Antoine Jan 10 '17 at 10:01
How to disaccept another answer and accept this one? :) – Frankie Drake Dec 28 '21 at 12:05

score 36 · Accepted Answer · answered Mar 02 '11 at 11:36

36

sorted(timestamps, key=lambda d: map(int, d.split('-')))

answered Mar 02 '11 at 11:36

jd.

10,338
3
44
55

4

Cool. Raises a `TypeError` in Python 3, though. – Tim Pietzcker Mar 02 '11 at 11:45
5

I don't have Python 3 installed, but would that be because map returns an iterable? In that case, the key function should be lambda d: tuple(map(int, d.split('-'))). – jd. Mar 02 '11 at 11:54
If you need the latest date in the array, you can add the `reverse=True` argument. – SeanFromIT Feb 01 '21 at 23:19

score 10 · Answer 3 · answered Mar 02 '11 at 11:40

Just doing that:

timestamps.sort()

result:

['2010-1-12',
 '2010-1-14',
 '2010-11-16',
 '2010-11-22',
 '2010-11-23',
 '2010-11-26',
 '2010-12-02',
 '2010-12-13',
 '2010-2-07',
 '2010-2-11',
 '2011-02-04',
 '2011-06-2',
 '2011-08-05',
 '2011-11-30']

The order year-month-day allow such a sorting because a day changes before a month and a month changes before a year when time is passing.

It's like for a number: the unity digit (the rightmost digit) changes before the ten digit, and this latter changes before the hundred digit, when 1 is progressively added.

And there is the fact that sort() processes from left to right : if the characters at one precise position are the same in two strings to sort, it will examine the two characters in the two string at the following position to decide which one is logically preceding.

Plus the fact that '0' < '1' is True, '1' < '2' is True etc

@Tim Pietzcker Oh yes. It only works if the numbers are zfilled(2) which is more frequently the case — eyquem, Mar 02 '11 at 12:01
and your result is wrong, because `'2010-2-07'` comes after `'2010-12-13'` , this is radix sort — Mohsen_Fatemi, Oct 17 '17 at 20:33

score 6 · Answer 4 · answered Mar 02 '11 at 11:41

>>> import time
>>> timestamps = ['2011-06-2', '2011-08-05', '2011-02-04', '2010-1-14', '2010-12-13', '2010-1-12', '2010-2-11', '2010-2-07', '2010-12-02', '2011-11-30', '2010-11-26', '2010-11-23', '2010-11-22', '2010-11-16']
>>> timestamps.sort(key=lambda x: time.mktime(time.strptime(x,"%Y-%m-%d")))
>>> timestamps
['2010-1-12', '2010-1-14', '2010-2-07', '2010-2-11', '2010-11-16', '2010-11-22', '2010-11-23', '2010-11-26', '2010-12-02', '2010-12-13', '2011-02-04', '2011-06-2', '2011-08-05', '2011-11-30']

score 2 · Answer 5 · answered Mar 02 '11 at 11:34

2

If you sort them into the same format you can just call timestamps.sort()

answered Mar 02 '11 at 11:34

Jakob Bowyer

32,237
8
73
89

pyanon · Answer 6 · 2011-03-14T21:50:31.300

1

map(lambda x:x[1], sorted(map(lambda a:[map(int,a.split('-')),a], timestamps)))

['2010-1-12',
 '2010-1-14',
 '2010-2-07',
 '2010-2-11',
 '2010-11-16',
 '2010-11-22',
 '2010-11-23',
 '2010-11-26',
 '2010-12-02',
 '2010-12-13',
 '2011-02-04',
 '2011-06-2',
 '2011-08-05',
 '2011-11-30']

edited Mar 14 '11 at 21:50

answered Mar 11 '11 at 22:27

pyanon

995
5
3

score 1 · Answer 7 · edited Feb 26 '20 at 17:43

1

print(sorted(list_of_strings,key=lambda x :(int(x.split('-')[0]),int(x.split('-')[1]),int(x.split('-')[2])))

edited Feb 26 '20 at 17:43

S.S. Anne

14,415
7
35
68

answered Feb 26 '20 at 17:23

bhanuprakash bhimarati

11
2

score 0 · Answer 8 · answered Apr 25 '18 at 06:51

This sort ascending dates in dd/mm/yyyy format

from datetime import datetime 
c_array=['07/12/2017', '30/01/2018', '31/05/2016', '30/09/2016', '30/01/2017', '31/05/2017']

sorted(c_array, key=lambda x: datetime.strptime(x, "%d/%m/%Y").strftime("%Y-%m-%d"))
#out: ['31/05/2016', '30/09/2016', '30/01/2017', '31/05/2017', '07/12/2017', '30/01/2018']

score 0 · Answer 9 · answered Nov 11 '18 at 07:51

In Python 3 and using (my personal favorite) comprehensions. For dates, I would always use Python's datetime lib:

timestamps = ['2011-06-2', '2011-08-05', '2011-02-04', '2010-1-14', '2010-12-13', '2010-1-12', '2010-2-11', '2010-2-07', '2010-12-02', '2011-11-30', '2010-11-26', '2010-11-23', '2010-11-22', '2010-11-
timestamps = [datetime.date(*[int(y) for y in x.split("-")]) for x in timestamps]
sorted_timestamps = sorted(timestamps)

sort dates in python array

9 Answers9

Linked

Related