# Python | Sort list elements by frequency

Given a list containing repeated and non-repeated elements, the task is to sort the given list on basis of the frequency of elements. Let’s discuss few methods for same.

Method #1: Using collections.counter()

 # Python code to demonstrate # sort list by frequency # of elements    from collections import Counter    ini_list = [1, 2, 3, 4, 4, 5, 5, 5, 5, 7,              1, 1, 2, 4, 7, 8, 9, 6, 6, 6]    # printing initial ini_list print ("initial list", str(ini_list))    # sorting on bais of frequency of elements result = [item for items, c in Counter(ini_list).most_common()                                       for item in [items] * c]    # printing final result print("final list", str(result))

Output:

initial list [1, 2, 3, 4, 4, 5, 5, 5, 5, 7, 1, 1, 2, 4, 7, 8, 9, 6, 6, 6]
final list [5, 5, 5, 5, 1, 1, 1, 4, 4, 4, 6, 6, 6, 2, 2, 7, 7, 3, 8, 9]

Method #2: Using iterables

 # Python code to demonstrate # sort list by frequency # of elements    from collections import Counter from itertools import repeat, chain    ini_list = [1, 2, 3, 4, 4, 5, 5, 5, 5, 7,             1, 1, 2, 4, 7, 8, 9, 6, 6, 6]    # printing initial ini_list print ("initial list", str(ini_list))    # sorting on bais of frequency of elements result = list(chain.from_iterable(repeat(i, c)          for i, c in Counter(ini_list).most_common()))    # printing final result print("final list", str(result))

Output:

initial list [1, 2, 3, 4, 4, 5, 5, 5, 5, 7, 1, 1, 2, 4, 7, 8, 9, 6, 6, 6]
final list [5, 5, 5, 5, 1, 1, 1, 4, 4, 4, 6, 6, 6, 2, 2, 7, 7, 3, 8, 9]

Method #3: Using sorted

 # Python code to demonstrate # sort list by frequency # of elements    from collections import Counter    ini_list = [1, 1, 2, 2, 2, 3, 3, 3, 3, 3,                5, 5, 5, 4, 4, 4, 4, 4, 4]    # printing initial ini_list print ("initial list", str(ini_list))    # sorting on bais of frequency of elements result = sorted(ini_list, key = ini_list.count,                                 reverse = True)    # printing final result print("final list", str(result))

Output:

initial list [1, 1, 2, 2, 2, 3, 3, 3, 3, 3, 5, 5, 5, 4, 4, 4, 4, 4, 4]
final list [4, 4, 4, 4, 4, 4, 3, 3, 3, 3, 3, 2, 2, 2, 5, 5, 5, 1, 1]

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