Sorting a list of dictionary values by date and time in python

Question

I want to sort the following data by date and time.

{'TID': 'B1', 'sno': '2', 'datetime': '04-13-12 17:21:18:83'}
{'TID': 'A1', 'sno': '4', 'datetime': '11-17-12 22:50:59:30'}
{'TID': 'A2', 'sno': '3', 'datetime': '11-17-12 22:51:00:66'}
{'TID': 'B6', 'sno': '2', 'datetime': '10-28-12 07:26:02:19'}
{'TID': 'B0', 'sno': '8', 'datetime': '02-26-16 08:13:01:30'}
{'TID': 'B4', 'sno': '8', 'datetime': '02-26-16 08:13:02:43'}
{'TID': 'C1', 'sno': '9', 'datetime': '03-08-15 17:12:55:81'}
{'TID': 'A2', 'sno': '23', 'datetime': '03-08-15 17:31:31:12'}

Solution proposed here and here don't work for me.

Hee is my code:

mylist=[]
with open(path+outfile) as fid:
    for line in fid:
        mylist.append(eval(line))


from operator import itemgetter
newlist = sorted(mylist, key=itemgetter('datetime')) 
for item in newlist:
    print(str(item))

here is the output of the above code:

 {'sno': '8', 'TID': 'B0', 'datetime': '02-26-16 08:13:01:30'}
{'sno': '8', 'TID': 'B4', 'datetime': '02-26-16 08:13:02:43'}
{'sno': '9', 'TID': 'C1', 'datetime': '03-08-15 17:12:55:81'}
{'sno': '23', 'TID': 'A2', 'datetime': '03-08-15 17:31:31:12'}
{'sno': '2', 'TID': 'B1', 'datetime': '04-13-12 17:21:18:83'}
{'sno': '2', 'TID': 'B6', 'datetime': '10-28-12 07:26:02:19'}
{'sno': '4', 'TID': 'A1', 'datetime': '11-17-12 22:50:59:30'}
{'sno': '3', 'TID': 'A2', 'datetime': '11-17-12 22:51:00:66'}

If you notice, the above output is not sorted by date and time.

If your `datetime` values were done properly, that other solution would work. — Stefan Pochmann, Jan 30 '17 at 08:27
I don't see how it is _not_ sorted. It is sorted alphabetically. Problem is: you have months first, so you need to parse the date first. — Jean-François Fabre, Jan 30 '17 at 08:28
@Jean-FrançoisFabre. I'm new to python. Can you help me to do that? — CKM, Jan 30 '17 at 08:30

Jean-François Fabre · Accepted Answer · 2017-01-30T08:49:35.030

alphanumerical sort doesn't work here because the date is month-day-year. For it to work properly it should be year-month-day. I defined an helper function to split the date elements and rebuild a tuple so natural tuple sort matches date sort:

def sortable_date(x):
    d,t = x['datetime'].split()
    dtoks = d.split('-')
    #        year     month    day     time
    return (dtoks[2],dtoks[0],dtoks[1],t)

result = sorted(data,key=sortable_date)

Another possibility would be to sort according to parsed date, like this:

result = sorted(data,key=lambda x : time.strptime(x['datetime'],"%m-%d-%y %H:%M:%S:%f"))

with your data I get:

{'TID': 'B1', 'datetime': '04-13-12 17:21:18:83', 'sno': '2'}
{'TID': 'B6', 'datetime': '10-28-12 07:26:02:19', 'sno': '2'}
{'TID': 'A1', 'datetime': '11-17-12 22:50:59:30', 'sno': '4'}
{'TID': 'A2', 'datetime': '11-17-12 22:51:00:66', 'sno': '3'}
{'TID': 'C1', 'datetime': '03-08-15 17:12:55:81', 'sno': '9'}
{'TID': 'A2', 'datetime': '03-08-15 17:31:31:12', 'sno': '23'}
{'TID': 'B0', 'datetime': '02-26-16 08:13:01:30', 'sno': '8'}
{'TID': 'B4', 'datetime': '02-26-16 08:13:02:43', 'sno': '8'}

I was relying on dateutil, but it failed me :D – Mohammad Yusuf Jan 30 '17 at 08:47 — Mohammad Yusuf, Jan 30 '17 at 08:47

score 2 · Answer 2 · answered Jan 30 '17 at 08:39

You can write your own key function to extract and parse the datetime:

import datetime
from operator import itemgetter

mylist = [{'TID': 'B1', 'sno': '2', 'datetime': '04-13-12 17:21:18:83'},
{'TID': 'A1', 'sno': '4', 'datetime': '11-17-12 22:50:59:30'},
{'TID': 'A2', 'sno': '3', 'datetime': '11-17-12 22:51:00:66'},
{'TID': 'B6', 'sno': '2', 'datetime': '10-28-12 07:26:02:19'},
{'TID': 'B0', 'sno': '8', 'datetime': '02-26-16 08:13:01:30'},
{'TID': 'B4', 'sno': '8', 'datetime': '02-26-16 08:13:02:43'},
{'TID': 'C1', 'sno': '9', 'datetime': '03-08-15 17:12:55:81'},
{'TID': 'A2', 'sno': '23', 'datetime': '03-08-15 17:31:31:12'}]

def key_function(item_dictionary):
    '''Extract datetime string from given dictionary, and return the parsed datetime object'''
    datetime_string = item_dictionary['datetime']
    return datetime.datetime.strptime(datetime_string, '%m-%d-%y %H:%M:%S:%f')

mylist.sort(key=key_function)

result:

[{'TID': 'B1', 'datetime': '04-13-12 17:21:18:83', 'sno': '2'},
 {'TID': 'B6', 'datetime': '10-28-12 07:26:02:19', 'sno': '2'},
 {'TID': 'A1', 'datetime': '11-17-12 22:50:59:30', 'sno': '4'},
 {'TID': 'A2', 'datetime': '11-17-12 22:51:00:66', 'sno': '3'},
 {'TID': 'C1', 'datetime': '03-08-15 17:12:55:81', 'sno': '9'},
 {'TID': 'A2', 'datetime': '03-08-15 17:31:31:12', 'sno': '23'},
 {'TID': 'B0', 'datetime': '02-26-16 08:13:01:30', 'sno': '8'},
 {'TID': 'B4', 'datetime': '02-26-16 08:13:02:43', 'sno': '8'}]

Sorting a list of dictionary values by date and time in python

2 Answers2