Sorting a list of strings with numbers in them in python

Question

So I have a list of string paths:

x = ['../../scene/temp_5a/458754/1_car.png',
     '../../scene/temp_5a/458754/2_car.png',
     '../../scene/temp_5a/458754/10_car.png',
     '../../scene/temp_5a/458754/15_car.png',
     '../../scene/temp_5a/458754/3_car.png']

And I need to sort it by the number in front of _car. Does anyone know of a quick way to do this?

I currently have this but it seems like the split is getting all the digits. I only want to get the digit in front in front of _car.

def atoi(text):
    return int(text) if text.isdigit() else text

def natural_keys(text):
    return [ atoi(c) for c in re.split('(\d+)', text) ]

x.sort(key=natural_keys) # gives an error

what was the error the last line gave you? I ran your code and got your desired sorted output with no error. — chickity china chinese chicken, Apr 19 '17 at 02:13
You're right! I had forgotten that x.sort() sorts the array in place, so it was outputting None and causing parts of my code to spit out garbage. Thanks! — jlcv, Apr 19 '17 at 02:24
Ah, yes, I know the feeling! good to hear you figured it out, glad to help. cheers! — chickity china chinese chicken, Apr 19 '17 at 02:26
Possible duplicate of [Does Python have a built in function for string natural sort?](http://stackoverflow.com/questions/4836710/does-python-have-a-built-in-function-for-string-natural-sort) — Alexei Levenkov, Apr 19 '17 at 02:40

score 1 · Answer 1 · answered Apr 19 '17 at 01:37

My way is to split the string and use the number in front of _car as key to make comparisons.

>>> x = [
...     '../../scene/temp_5a/458754/1_car.png',
...     '../../scene/temp_5a/458754/2_car.png',
...     '../../scene/temp_5a/458754/10_car.png',
...     '../../scene/temp_5a/458754/15_car.png',
...     '../../scene/temp_5a/458754/3_car.png']
>>>
>>> sorted(x,key=lambda i: int(i.split('/')[-1].split('_')[0]))
[[1, '../../scene/temp_5a/458754/1_car.png'], [2, '../../scene/temp_5a/458754/2_car.png'], [3, '../../scene/temp_5a/458754/3_car.png'], [10, '../../scene/temp_5a/458754/10_car.png'], [15, '../../scene/temp_5a/458754/15_car.png']]

score 1 · Answer 2 · answered Apr 19 '17 at 01:37

x = ['../../scene/temp_5a/458754/1_car.png',
'../../scene/temp_5a/458754/2_car.png',
'../../scene/temp_5a/458754/10_car.png',
'../../scene/temp_5a/458754/15_car.png',
'../../scene/temp_5a/458754/3_car.png']
sorted(x,key=lambda x: int(x.split('/')[-1].split('_car')[0]))

Out[118]: 
['../../scene/temp_5a/458754/1_car.png',
 '../../scene/temp_5a/458754/2_car.png',
 '../../scene/temp_5a/458754/3_car.png',
 '../../scene/temp_5a/458754/10_car.png',
 '../../scene/temp_5a/458754/15_car.png']

chickity china chinese chicken · Accepted Answer · 2017-04-19T02:11:55.923

I'm not sure why your regex gave you an error, it worked for me. Maybe try a different regex?

Replacing yours with r'.*\/([^_]*)_.*' may also work:

x = ['../../scene/temp_5a/458754/1_car.png',
'../../scene/temp_5a/458754/2_car.png',
'../../scene/temp_5a/458754/10_car.png',
'../../scene/temp_5a/458754/15_car.png',
'../../scene/temp_5a/458754/3_car.png']

def atoi(text):
return int(text) if text.isdigit() else text

def natural_keys(text):
    return [ atoi(c) for c in re.split(r'.*\/([^_]*)_.*', text) ]

x.sort(key=natural_keys)
print x

output:

['../../scene/temp_5a/458754/1_car.png',  
'../../scene/temp_5a/458754/2_car.png', 
'../../scene/temp_5a/458754/3_car.png', 
'../../scene/temp_5a/458754/10_car.png', 
'../../scene/temp_5a/458754/15_car.png']

score 1 · Answer 4 · answered Apr 19 '17 at 01:59

String matching is what regex does. Requires very little regex.

import re

x = ['../../scene/temp_5a/458754/1_car.png',
     '../../scene/temp_5a/458754/2_car.png',
     '../../scene/temp_5a/458754/10_car.png',
     '../../scene/temp_5a/458754/15_car.png',
     '../../scene/temp_5a/458754/3_car.png']


def file_matcher(files):
    numbers = []
    for f in files:
        match = re.search(r'([0-9]+)_car.png', f)
        numbers.append(match.group(1))
    return numbers

print file_matcher(x)

Sorting a list of strings with numbers in them in python

4 Answers4

Linked