Remove duplicates from a list in-place

Question

How can one make a list contain only unique items while preserving order AND updating it in-place?

I know that a set can be used, but it will not guarantee ordering.

Answer 1

Use a supporting set, and a while loop:

def unique(arr):
    tmp_set = set()
    i = 0
    while i < len(arr):
        if arr[i] in tmp_set:
            del arr[i]
        else:
            tmp_set.add(arr[i])
            i += 1

The above will update the array in-place, and preserve ordering of the elements as well.