Python cap number of occurences of duplicate items in a list

I’m looking for a function to limit the number of duplicates in a list. For example in the list below, we have three ‘1’s, one ‘2’, two ‘a’s, and three ‘b’s.

initial_list = [1,2,1,1,'a','b','a', 'b','b']

def cap(initial_list, n=2)

If I was to limit the number of duplicates to n=2, I would get:

[1,2,1,'a','b','a', 'b']

The order of the items in the output does not matter.

>Solution :

You need to keep track of the number of values enountered. You can use dictionary for this (defaultdict even better):

from collections import defaultdict

def cap(initial_list, n=2):
    counter = defaultdict(int)
    result = []
    for e in initial_list:
        if counter[e] < n:
            result.append(e)
        counter[e] += 1
    return result

initial_list = [1,2,1,1,'a','b','a', 'b','b']
cap(initial_list)

output:

[1, 2, 1, 'a', 'b', 'a', 'b']