Python | Delete elements with frequency atmost K

There are many methods that can be employed to perform the deletion in the list. Be it remove function, pop function and many other functions. But most of the times, we usually don’t deal with the simple deletion, but with certain constraints. This article discusses certain ways in which we can delete only those elements which occurs less than K times.

Method #1 : Using list comprehension + count()
The idea applied here is to construct a new list using list comprehension and insert only those elements which occur more than K times. The count operation is done with the help of count function.

# Python3 code to demonstrate 
# remove elements less than and equal K  
# using list comprehension + count() 
  
# initializing list 
test_list = [1, 4, 3, 2, 3, 3, 2, 2, 2, 1] 
  
# printing original list 
print("The original list : " + str(test_list)) 
  
# initializing K 
K = 2
  
# using list comprehension + count() 
# remove elements less than K  
res = [ i for i in test_list if test_list.count(i) > K] 
  
# print result 
print("The list removing elements less than and equal K  : " + str(res)) 

Output :

The original list : [1, 4, 3, 2, 3, 3, 2, 2, 2, 1]
The list removing elements less than and equal K  : [3, 2, 3, 3, 2, 2, 2]

Method #2 : Using Counter() + list comprehension
This problem can be efficiently solved using the Counter function that precomputes the count of each elements in list so that the decision to keep or reject a particular element takes lesser time.

# Python3 code to demonstrate 
# remove elements less than and equal K  
# using Counter() + list comprehension 
from collections import Counter 
  
# initializing list 
test_list = [1, 4, 3, 2, 3, 3, 2, 2, 2, 1] 
  
# printing original list 
print("The original list : " + str(test_list)) 
  
# initializing K 
K = 2
  
# using Counter() + list comprehension 
# remove elements less than K  
freq = Counter(test_list) 
res = [ele for ele in test_list if freq[ele] > K] 
  
# print result 
print("The list removing elements less than and equal K  : " + str(res)) 

Output :

The original list : [1, 4, 3, 2, 3, 3, 2, 2, 2, 1]
The list removing elements less than and equal K  : [3, 2, 3, 3, 2, 2, 2]

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