Python - Descending Sort String Numbers

Reverse Sorting a list is easy task and has been dealt with in many situations. With Machine Learning and Data Science emerging, sometimes we can get the data in the format of list of numbers but with string as data type. Generic Sort functions give erroneous result in that case, hence several other methods have to employed to perform these particular task. Lets discuss ways in which this is performed. 

Method #1 : Naive Method In the naive method requires the type conversion of all the elements into integers of the list iterated through a loop. After that generic sort function is employed to perform the task. The descending sorting is done by passing reverse. 

# Python3 code to demonstrate 
# Descending Sort String Numbers
# using naive method 

# initializing list 
test_list = [ '4', '6', '7', '2', '1']

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

# Descending Sort String Numbers
# numeric string sorting
for i in range(0, len(test_list)) :
    test_list[i] = int(test_list[i])
test_list.sort(reverse = True)

# printing result
print ("The resultant reverse sorted list : " + str(test_list))

The original list is : ['4', '6', '7', '2', '1']
The resultant reverse sorted list : [7, 6, 4, 2, 1]

Time complexity: O(nlogn), where n is the length of the test_list. 
Auxiliary Space: O(n), extra space of size n is required

  Method #2 : Using sort() using key + reverse The generic sort() can be used to perform this particular task, but has to be specified with the key as integer to convert it to integer while performing sort function internally. The descending sorting is done by passing reverse. 

# Python3 code to demonstrate 
# Descending Sort String Numbers
# using sort() + key

# initializing list 
test_list = [ '4', '6', '7', '2', '1']

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

# using sort() + key
# Descending Sort String Numbers
test_list.sort(key = int, reverse = True)

# printing result
print ("The resultant reverse sorted list : " + str(test_list))

The original list is : ['4', '6', '7', '2', '1']
The resultant reverse sorted list : ['7', '6', '4', '2', '1']

Time Complexity: O(n*nlogn), where n is the number of elements in the list “test_list”.
Auxiliary Space: O(n), where n is the number of elements in the list “test_list”.

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Article Tags :

• Python
• Python Programs
• Python list-programs
• Python-sort

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