Python – Sort List items on basis of their Digits

Given List of elements, perform sorting on basis of digits of numbers.

Input : test_list = [434, 211, 12, 3] Output : [12, 211, 3, 434] Explanation : 3 < 12, still later in list, as initial digit, 1 < 3. Hence sorted by digits rather than number. Input : test_list = [534, 211, 12, 7] Output : [12, 211, 534, 7] Explanation : 7 < 534, still later in list, as initial digit, 5 < 7. Hence sorted by digits rather than number.

Method #1 : Using map() + str() + ljust() + sorted()

In this, the list elements are converted into string using map() and str(), ljust() is used to append constant character to make each number equal length. Then sort is performed using sorted().

Python3

# Python3 code to demonstrate working of
# Sort List by Digits
# Using map() + str() + ljust() + sorted()

# initializing list
test_list = [434, 211, 12, 54, 3]

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

# converting elements to string
temp1 = map(str, test_list)

# getting max length
max_len = max(map(len, temp1))

# performing sort operation
res = sorted(test_list, key = lambda idx : (str(idx).ljust(max_len, 'a')))

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

Output

The original list is : [434, 211, 12, 54, 3]
List after sorting : [12, 211, 3, 434, 54]

Time Complexity: O(nlogn) where n is the number of elements in the list “test_list”. 
Auxiliary Space: O(1), additional space is not needed.

Method #2 : Using list comprehension + sorted() + lambda

In this, we as parameter to sorted(),  pass a list of digits. Performing sort according to that gives desired results.

Python3

# Python3 code to demonstrate working of
# Sort List by Digits
# Using list comprehension + sorted() + lambda

# initializing list
test_list = [434, 211, 12, 54, 3]

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

# performing sort operation
# converting number to list of Digits
res = sorted(test_list, key = lambda ele: [int(j) for j in str(ele)])

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

Output

The original list is : [434, 211, 12, 54, 3]
List after sorting : [12, 211, 3, 434, 54]