How to remove duplicates from a list using this function?

Question

I'm new to python. Could someone help me understand why the following function doesn't work? It is supposed to return a new list with the duplicates removed but instead prints [4,6].

def remove_duplicates(l):
    solution = []
    for item in l:
        if l.count(item) < 2:
            solution.append(item)
        else:
            l.remove(item)
    return solution


print (remove_duplicates([4,5,5,5,4,6]))

I thought it iterates one item at a time in a list. So the first 5 would have a count of 3 and be remove, the second five would have a count of 2 and be removed and the third 5 would have a count of 1 and be appended to the solution list. I can't wrap my head around why the 5s would be completely removed but the 4s would not.

Possible duplicate of [How do you remove duplicates from a list whilst preserving order?](https://stackoverflow.com/questions/480214/how-do-you-remove-duplicates-from-a-list-whilst-preserving-order) — Arkistarvh Kltzuonstev, Oct 05 '19 at 19:55
This [graphic](https://stackoverflow.com/questions/6500888/removing-from-a-list-while-iterating-over-it) might help you better understand whats going on. — Darjusch, Oct 05 '19 at 20:04

score 0 · Answer 1 · edited Oct 05 '19 at 20:16

0

Use set data type in python to remove the duplicates.

a = [4,5,5,5,4,6]
solution = list(set(a))

Output:

[4,5,6]

edited Oct 05 '19 at 20:16

Olvin Roght

7,677
2
16
35

answered Oct 05 '19 at 19:53

Rajeshkumar

59
1
1
9

score 0 · Answer 2 · answered Oct 05 '19 at 19:58

You must not remove items from a list, you are iterating at the moment. Iterating is done by incrementing an index internally.

If you want to keep the last occurence of an item, best, count them at first:

from collections import Counter
def remove_duplicates(l):
    solution = []
    counts = Counter(l)
    for item in l:
        if counts[item] == 1:
            solution.append(item)
        else:
            counts[item] -= 1
    return solution

How to remove duplicates from a list using this function?

2 Answers2