How to remove elements from a list that appear less than k = 2?

I am trying to keep elements of a list that appear at least twice, and remove the elements that appear less than twice.

For example, my list can look like:

letters = [‘a’, ‘a’, ‘b’, ‘b’, ‘b’, ‘c’]

I want to get a list with the numbers that appear at least twice, to get the following list:

letters_appear_twice = [‘a’, ‘b’].

But since this is part of a bigger code, I don’t know exactly what my lists looks like, only that I want to keep the letters that are repeated at least twice. But for the sake of understanding, we can assume I know what the list looks like!

I have tried the following:

”’

letters = ['a', 'a', 'b', 'b', 'b', 'c']

for x in set(letters):
    if letters.count(x) > 2:
        while x in letters:
            letters.remove(x)

print(letters)

”’

But this doesn’t quite work like I want it too…

Thank you in advance for any help!

>Solution :

letters = ['a', 'a', 'b', 'b', 'b', 'c']

res  = []
for x in set(letters):
    if letters.count(x) >= 2:
        res.append(x)
print(res)

Prints:

['b', 'a']