CODEWITHSUNDEEP
pythonlistsortingprefix
user248237
user248237

Reputation:

sorting list in python

if I have a list of strings e.g. ["a143.txt", "a9.txt", ] how can I sort it in ascending order by the numbers in the list, rather than by the string. I.e. I want "a9.txt" to appear before "a143.txt" since 9 < 143.

thanks.

Upvotes: 8

Views: 2475

Answers (5)

Prydie
Prydie

Reputation: 1827

list.sort() is deprecated (see Python.org How-To) . sorted(list, key=keyfunc) is better.

import re

def sortFunc(item):
  return int(re.search(r'[a-zA-Z](\d+)', item).group(1))

myList = ["a143.txt", "a9.txt"]

print sorted(myList, key=sortFunc)

Upvotes: 0

tokland
tokland

Reputation: 67860

>>> paths = ["a143.txt", "a9.txt"]
>>> sorted(paths, key=lambda s: int(re.search("\d+", s).group()))
['a9.txt', 'a143.txt']

More generic, if you want it to work also for files like: a100_32_12 (and sorting by numeric groups):

>>> paths = ["a143_2.txt", "a143_1.txt"]
>>> sorted(paths, key=lambda s: map(int, re.findall("\d+", s)))
['a143_1.txt', 'a143_1.txt']

Upvotes: 0

highBandWidth
highBandWidth

Reputation: 17321

If you want to completely disregard the strings, then you should do

import re
numre = re.compile('[0-9]+')
def extractNum(s):
    return int(numre.search(s).group())

myList = ["a143.txt", "a9.txt", ]
myList.sort(key=extractNum)

Upvotes: 0

bradley.ayers
bradley.ayers

Reputation: 38382

Use list.sort() and provide your own function for the key argument. Your function will be called for each item in the list (and passed the item), and is expected to return a version of that item that will be sorted.

See http://wiki.python.org/moin/HowTo/Sorting/#Key_Functions for more information.

Upvotes: 0

wmil
wmil

Reputation: 3189

It's called "natural sort order", From http://www.codinghorror.com/blog/2007/12/sorting-for-humans-natural-sort-order.html

Try this:

import re 

def sort_nicely( l ): 
  """ Sort the given list in the way that humans expect. 
  """ 
  convert = lambda text: int(text) if text.isdigit() else text 
  alphanum_key = lambda key: [ convert(c) for c in re.split('([0-9]+)', key) ] 
  l.sort( key=alphanum_key )

Upvotes: 14

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