Sort a sublist of elements in a list leaving the rest in place

Question

Say I have a sorted list of strings as in:

[\'A\', \'B\' , \'B1\', \'B11\', \'B2\', \'B21\', \'B22\', \'C\', \'C1\', \'C11\', \'C2\']

Now I wan

Answer 1

You can use the following key function. It will return a tuple of the form (letter, number) if there is a number, or of the form (letter,) if there is no number. This works since ('A',) < ('A', 1).

import re

a = ['A', 'B' ,'B1', 'B11', 'B2', 'B21', 'B22', 'C', 'C1', 'C11', 'C2']

regex = re.compile(r'(\d+)')

def order(e):
    num = regex.findall(e)
    if num:
        num = int(num[0])
        return e[0], num
    return e,

print(sorted(a, key=order))
>> ['A', 'B', 'B1', 'B2', 'B11', 'B21', 'B22', 'C', 'C1', 'C2', 'C11']