How to sort alpha numeric set in python


I have a set

set(['booklet', '4 sheets', '48 sheets', '12 sheets'])

After sorting I want it to look like

4 sheets,
12 sheets,
48 sheets,

Any idea please

Asked By: mmrs151



>>> a = set(['booklet', '4 sheets', '48 sheets', '12 sheets'])
>>> def ke(s):
    i, sp, _ = s.partition(' ')
    if i.isnumeric():
        return int(i)
    return float('inf')

>>> sorted(a, key=ke)
['4 sheets', '12 sheets', '48 sheets', 'booklet']
Answered By: SilentGhost

sets are inherently un-ordered. You’ll need to create a list with the same content and sort that.

Answered By: Rakis

Based on SilentGhost’s answer:

In [4]: a = set(['booklet', '4 sheets', '48 sheets', '12 sheets'])

In [5]: def f(x):
   ...:     num = x.split(None, 1)[0]
   ...:     if num.isdigit():
   ...:         return int(num)
   ...:     return x

In [6]: sorted(a, key=f)
Out[6]: ['4 sheets', '12 sheets', '48 sheets', 'booklet']
Answered By: draebek

Jeff Atwood talks about natural sort and gives an example of one way to do it in Python. Here is my variation on it:

import re 

def sorted_nicely( l ): 
    """ Sort the given iterable 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) ] 
    return sorted(l, key = alphanum_key)

Use like this:

s = set(['booklet', '4 sheets', '48 sheets', '12 sheets'])
for x in sorted_nicely(s):


4 sheets
12 sheets
48 sheets

One advantage of this method is that it doesn’t just work when the strings are separated by spaces. It will also work for other separators such as the period in version numbers (for example 1.9.1 comes before 1.10.0).

Answered By: Mark Byers

A simple way is to split up the strings to numeric parts and non-numeric parts and use the python tuple sort order to sort the strings.

import re
tokenize = re.compile(r'(d+)|(D+)').findall
def natural_sortkey(string):          
    return tuple(int(num) if num else alpha for num, alpha in tokenize(string))

sorted(my_set, key=natural_sortkey)
Answered By: Ants Aasma

Short and sweet:

sorted(data, key=lambda item: (int(item.partition(' ')[0])
                               if item[0].isdigit() else float('inf'), item))

This version:

  • Works in Python 2 and Python 3, because:
    • It does not assume you compare strings and integers (which won’t work in Python 3)
    • It doesn’t use the cmp parameter to sorted (which doesn’t exist in Python 3)
  • Will sort on the string part if the quantities are equal

If you want printed output exactly as described in your example, then:

data = set(['booklet', '4 sheets', '48 sheets', '12 sheets'])
r = sorted(data, key=lambda item: (int(item.partition(' ')[0])
                                   if item[0].isdigit() else float('inf'), item))
print ',n'.join(r)
Answered By: Daniel Stutzbach

It was suggested that I repost this answer over here since it works nicely for this case also

from itertools import groupby
def keyfunc(s):
    return [int(''.join(g)) if k else ''.join(g) for k, g in groupby(s, str.isdigit)]

sorted(my_list, key=keyfunc)


>>> my_set = {'booklet', '4 sheets', '48 sheets', '12 sheets'}
>>> sorted(my_set, key=keyfunc)
['4 sheets', '12 sheets', '48 sheets', 'booklet']

For Python3 it’s necessary to modify it slightly (this version works ok in Python2 too)

def keyfunc(s):
    return [int(''.join(g)) if k else ''.join(g) for k, g in groupby(''+s, str.isdigit)]
Answered By: John La Rooy

For people stuck with a pre-2.4 version of Python, without the wonderful sorted() function, a quick way to sort sets is:

l = list(yourSet)

This does not answer the specific question above (12 sheets will come before 4 sheets), but it might be useful to people coming from Google.

Answered By: Giacomo Lacava

You should check out the third party library natsort. Its algorithm is general so it will work for most input.

>>> import natsort
>>> your_list = set(['booklet', '4 sheets', '48 sheets', '12 sheets'])
>>> print ',n'.join(natsort.natsorted(your_list))
4 sheets,
12 sheets,
48 sheets,
Answered By: SethMMorton

Generic answer to sort any numbers in any position in an array of strings. Works with Python 2 & 3.

def alphaNumOrder(string):
   """ Returns all numbers on 5 digits to let sort the string with numeric order.
   Ex: alphaNumOrder("a6b12.125")  ==> "a00006b00012.00125"
   return ''.join([format(int(x), '05d') if x.isdigit()
                   else x for x in re.split(r'(d+)', string)])


s = ['a10b20','a10b1','a3','b1b1','a06b03','a6b2','a6b2c10','a6b2c5']
s ===> ['a3', 'a6b2', 'a6b2c5', 'a6b2c10', 'a06b03', 'a10b1', 'a10b20', 'b1b1']

Part of the answer is from there

Answered By: Le Droid
b = set(['booklet', '10-b40', 'z94 boots', '4 sheets', '48 sheets',
         '12 sheets', '1 thing', '4a sheets', '4b sheets', '2temptations'])

numList = sorted([x for x in b if x.split(' ')[0].isdigit()],
                 key=lambda x: int(x.split(' ')[0]))

alphaList = sorted([x for x in b if not x.split(' ')[0].isdigit()])

sortedList = numList + alphaList


Out: ['1 thing',
      '4 sheets',
      '12 sheets',
      '48 sheets',
      '4a sheets',
      '4b sheets',
      'z94 boots']
Answered By: tldr
Categories: questions Tags: ,
Answers are sorted by their score. The answer accepted by the question owner as the best is marked with
at the top-right corner.