Sorting negative integer strings in python

Question

def sort_int_string(this_string):
    split_str = this_string.split()
    split_str.sort()
    join_str = ' '.join(split_str)
    return join_str

>>>print(sort_int_string("4 1 -1 -3"))
-1 -3 1 4

This code is meant to produce the proper order of "-3 -1" but for some reason I am getting this output where positive numbers are correct but the negatives are not. Any insight on what I am doing wrong? Thanks!

That code won't generate that output. Please always copy and paste transcripts exactly, rather than write what you guess it should do. — DSM
– DSM, Commented Jan 29, 2015 at 21:40
@DSM -- I'm always amazed at how quickly you pick up on small nuances like OP forgot to bind the return value of sorted. You're a machine sir! — mgilson
– mgilson, Commented Jan 29, 2015 at 21:42
@DSM -- Sorry. Im new to this stackoverflow thing! I repasted it exactly how I have it but I changed the sorted() to list.sort(). It still does not do what I want though. Any clue why? — felicia_rae
– felicia_rae, Commented Jan 29, 2015 at 21:47

Martijn Pieters · Accepted Answer · 2015-01-29 21:48:14Z

2

You are sorting strings, not numbers, and those are sorted lexicographically; like words in a dictionary. - happens to be sorted before digits, but '1' is still sorted before '3'. Furthermore, '10' sorts before '2' because '1' comes before '2' in a character table.

Sort numerically by converting each element to an integer while sorting:

split_str.sort(key=int)

Demo, with your corrected function:

>>> def sort_int_string(this_string):
...     split_str = this_string.split()
...     split_str.sort(key=int)
...     join_str = ' '.join(split_str)
...     return join_str
... 
>>> print(sort_int_string("4 1 -1 -3"))
-3 -1 1 4

edited Jan 29, 2015 at 21:48

answered Jan 29, 2015 at 21:42

Martijn Pieters

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Comments

dawg · Accepted Answer · 2015-01-29 21:58:44Z

0

You can use a regex:

>>> import re
>>> sorted(re.findall(r'-?\d+', "4 1 -1 -3"), key=int)
['-3', '-1', '1', '4']

That produces the strings in sorted order by their value.

You can rejoin into a string:

>>> sor=sorted(re.findall(r'-?\d+', "4 1 -1 -3"), key=int)
>>> ' '.join(sor)
'-3 -1 1 4'

answered Jan 29, 2015 at 21:58

dawg

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