Given a list of integers (elements may be repeated), write a Python program to remove the elements that are repeated less than k times.
Examples:
Input : lst = ['a', 'a', 'a', 'b', 'b', 'c'], k = 2 Output : ['a', 'a', 'a', 'b', 'b'] Input : lst = [1, 1, 1, 1, 2, 2, 3, 3, 3, 4, 4], k = 3 Output : [1, 1, 1, 1, 3, 3, 3]
Approach #1 : Pythonic naive
Counter()
from collections module
construct a dictionary mapping values to counts and save them in ‘counted’. Then we make use of ‘temp_lst’ to store the elements that need to be removed. Finally, we traverse through the given list and append all elements that are not in ‘temp_lst’ to ‘res_lst’ containing the required output.
# Python3 program to Remove elements of # list that repeated less than k times from collections import Counter def removeElements(lst, k): counted = Counter(lst) temp_lst = [] for el in counted: if counted[el] < k: temp_lst.append(el) res_lst = [] for el in lst: if el not in temp_lst: res_lst.append(el) return (res_lst) # Driver code lst = [ 'a' , 'a' , 'a' , 'b' , 'b' , 'c' ] k = 2 print (removeElements(lst, k)) |
['a', 'a', 'a', 'b', 'b']
Approach #2 : Efficient Approach
The efficient approach to use Counter method is to construct a dictionary mapping value to counts and then use a list comprehension to filter for counts larger than a specified value. This approach is both time and space efficient.
# Python3 program to Remove elements of # list that repeated less than k times from collections import Counter def removeElements(lst, k): counted = Counter(lst) return [el for el in lst if counted[el] > = k] # Driver code lst = [ 'a' , 'a' , 'a' , 'b' , 'b' , 'c' ] k = 2 print (removeElements(lst, k)) |
['a', 'a', 'a', 'b', 'b']
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