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Python – Sort List items on basis of their Digits
  • Last Updated : 05 Sep, 2020

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().



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# 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))

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Output

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

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.

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# 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))

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Output

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

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