Python | Sort alternate numeric and alphabet list

Sometimes, while performing sorting in list, we have a problem in which we need to perform particular type of sorting in which we need to sort in alternate ways in which we have numerics and alphabets sorted in order. Lets discuss certain ways in which this task can be performed. 

Method #1 : Using isalpha() + isnumeric() + zip_longest() The combination of above methods can be used to perform this task. In this, we separate the numeric and alphabets and then perform a sort on them separately and join using zip_longest(). 

Python3

# Python3 code to demonstrate
# Sort alternate numeric and alphabet list
# using isalpha() + isnumeric() + zip_longest()
from itertools import zip_longest

# Initializing list
test_list = ['3', 'B', '2', 'A', 'C', '1']

# printing original list
print("The original list is : " + str(test_list))

# Sort alternate numeric and alphabet list
# using isalpha() + isnumeric() + zip_longest()
num_list = sorted(filter(str.isnumeric, test_list),
                       key = lambda sub: int(sub))

chr_list = sorted(filter(str.isalpha, test_list))
res = [ele for sub in zip_longest(num_list, chr_list)
                              for ele in sub if ele]

# printing result
print ("List after performing sorting : " + str(res))

Output : 

The original list is : ['3', 'B', '2', 'A', 'C', '1']
List after performing sorting : ['1', 'A', '2', 'B', '3', 'C']

Method #2 : Using sorted() + key + lambda + isnumeric() The combination of above methods can be used to perform this task. In this, we perform the sorting in alternate manner using ord() and lambda function, testing using isnumeric(). 

Python3

# Python3 code to demonstrate
# Sort alternate numeric and alphabet list
# using sorted() + key + lambda + isnumeric()
from itertools import zip_longest

# Initializing list
test_list = ['3', 'B', '2', 'A', 'C', '1']

# printing original list
print("The original list is : " + str(test_list))

# Sort alternate numeric and alphabet list
# using sorted() + key + lambda + isnumeric()
res = sorted(test_list, key = lambda ele : (int(ele), 0)
      if ele.isnumeric()
      else ((ord(ele) - 64) % 26, 1))

# printing result
print ("List after performing sorting : " + str(res))

Output : 

The original list is : ['3', 'B', '2', 'A', 'C', '1']
List after performing sorting : ['1', 'A', '2', 'B', '3', 'C']

Method #3: 

• Split the list into two lists: one for digits and one for characters.
• Sort the lists using the built-in sort() function.
• Interleave the sorted lists and create the final result list.

Python3

# Python3 code to demonstrate
# Sort alternate numeric and alphabet list

# Initializing list
test_list = ['3', 'B', '2', 'A', 'C', '1']

# printing original list
print("The original list is : " + str(test_list))

# Split the list into digits and characters
digits = [x for x in test_list if x.isdigit()]
chars = [x for x in test_list if x.isalpha()]

# Sort the lists
digits.sort()
chars.sort()

# Interleave the sorted lists
res = [None] * len(test_list)
for i in range(len(test_list)):
    if i % 2 == 0:
        res[i] = digits[i//2]
    else:
        res[i] = chars[i//2]

# printing result
print ("List after performing sorting : " + str(res))

Output

The original list is : ['3', 'B', '2', 'A', 'C', '1']
List after performing sorting : ['1', 'A', '2', 'B', '3', 'C']

Time complexity: O(nlogn)

Auxiliary Space:O(n)