Python – Sort Strings by maximum frequency character

Given a string, the task is to write a Python program to perform sort by maximum occurring character.

Input : test_list = [“geekforgeeks”, “bettered”, “for”, “geeks”] 
Output : [‘for’, ‘geeks’, ‘bettered’, ‘geekforgeeks’] 
Explanation : 1 < 2 < 3 < 4, is ordering of maximum character occurrence frequency.

Input : test_list = [“geekforgeeks”, “for”, “geeks”] 
Output : [‘for’, ‘geeks’, ‘geekforgeeks’] 
Explanation : 1 < 2 < 4, is ordering of maximum character occurrence frequency. 

Method #1 : Using sort() + Counter() + max()

In this, we perform inplace sorting using sort(), and Counter() is used to compute characters frequency, max() used to get maximum of computed frequencies.

Python3

# Python3 code to demonstrate working of
# Sort Strings by maximum frequency character
# Using sort() + Counter() + max()
from collections import Counter

# getting maximum character frequency
def max_freq(arg_str):
    res = Counter(arg_str)
    return arg_str.count(max(res, key = res.get))

# initializing list
test_list = ["geekforgeeks", "bettered", "for", "geeks"]

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

# performing sort
test_list.sort(key = max_freq)

# printing result
print("Sorted List : " + str(test_list))

Output:

The original list is : ['geekforgeeks', 'bettered', 'for', 'geeks']
Sorted List : ['for', 'geeks', 'bettered', 'geekforgeeks']

Method #2 : Using sorted() + lambda + Counter()

In this, we perform the task of performing sort using sorted(), and lambda function to get a single statement logical expression, avoiding external function call.

Python3

# Python3 code to demonstrate working of
# Sort Strings by maximum frequency character
# Using sorted() + lambda + Counter()
from collections import Counter

# getting maximum character frequency
def max_freq(arg_str):
    res = Counter(arg_str)
    return arg_str.count(max(arg_str, key = arg_str.get))

# initializing list
test_list = ["geekforgeeks", "bettered", "for", "geeks"]

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

# performing sort
# lambda function to drive logic
res = sorted(test_list,
             key = lambda arg_str : arg_str.count(
               max(Counter(arg_str), key = Counter(arg_str).get)))

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

Output:

The original list is : ['geekforgeeks', 'bettered', 'for', 'geeks']
Sorted List : ['for', 'geeks', 'bettered', 'geekforgeeks']

The time and space complexity for all the methods are the same:

Time Complexity: O(n)

Space Complexity: O(n)

 Using dictionary and sorting:

Approach:

In this approach, we first create a dictionary that stores the count of the most occurring character for each string. Then, we sort the list based on the values of this dictionary. If two or more strings have the same count of the most occurring character, we sort them based on their original order in the input list.

Python3

def max_char_freq(string):
    freq_dict = {}
    for s in string:
        max_char = max(set(s), key=s.count)
        freq_dict[s] = s.count(max_char)
    return freq_dict

def sort_by_max_freq(string_list):
    freq_dict = max_char_freq(string_list)
    return sorted(string_list, key=lambda x: (freq_dict[x], string_list.index(x)))

test_list = ["geekforgeeks", "bettered", "for", "geeks"]
print(sort_by_max_freq(test_list))  # Output: ['for', 'geeks', 'bettered', 'geekforgeeks']

Output

['for', 'geeks', 'bettered', 'geekforgeeks']

Time Complexity: O(nlogn) where n is the length of the input list
Space Complexity: O(n)