Sort list of date strings

Question

I have an arbitrary list of date strings (mm-yyyy) as follows:

d = ['09-2012', '04-2007', '11-2012', '05-2013', '12-2006', '05-2006', '08-2007'...] 

I need this list to be sorted first by the level of years (ascending), then on the level of months (ascending)..so that the logical ordering can be:

d_ordered = ['05-2006', '12-2006', '04-2007', '08-2007', '09-2012', '11-2012', '05-2013' ...] 

How can I achieve this?

Answer 1

Try this:

import datetime d = ['09-2012', '04-2007', '11-2012', '05-2013', '12-2006', '05-2006', '08-2007'] sorted(d, key=lambda x: datetime.datetime.strptime(x, '%m-%Y')) 

Answer 2

Use sorted() with a key:

>>> d = ['09-2012', '04-2007', '11-2012', '05-2013', '12-2006', '05-2006', '08-2007'] >>> def sorting(L): ...     splitup = L.split('-') ...     return splitup[1], splitup[0] ...  >>> sorted(d, key=sorting) ['05-2006', '12-2006', '04-2007', '08-2007', '09-2012', '11-2012', '05-2013'] 

It's better to use a function here instead of a lambda to prevent calling split() twice (and it looks a bit neater :))

Note that this will return the sorted list. If you want to sort it in place, use .sort():

>>> d.sort(key=sorting) >>> d ['05-2006', '12-2006', '04-2007', '08-2007', '09-2012', '11-2012', '05-2013']