# How to sort alpha numeric set in python

## Question:

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,
booklet
``````

``````>>> 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']
``````

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

``````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']
``````

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):
print(x)
``````

Output:

``````4 sheets
12 sheets
48 sheets
booklet
``````

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).

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)
``````

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)
``````

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)
``````

Demo:

``````>>> 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)]
``````

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)
l.sort()
``````

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.

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,
booklet
``````

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)])
``````

Sample:

``````s = ['a10b20','a10b1','a3','b1b1','a06b03','a6b2','a6b2c10','a6b2c5']
s.sort(key=alphaNumOrder)
s ===> ['a3', 'a6b2', 'a6b2c5', 'a6b2c10', 'a06b03', 'a10b1', 'a10b20', 'b1b1']
``````

Part of the answer is from there

``````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

print(sortedList)

Out: ['1 thing',
'4 sheets',
'12 sheets',
'48 sheets',
'10-b40',
'2temptations',
'4a sheets',
'4b sheets',
'booklet',
'z94 boots']
``````
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