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()

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# 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))

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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

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# 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))

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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

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# 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))

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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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