Question

What i have only removes duplicated items and sorts them. I need to remove one instance of every item and return a new list with the items in it. This is what i have:

def rem(nlst):
    n = []
    for x in nlst:
        if x not in n:
            n.append(x)
            n.sort()
    return n

This is what it should do:

>>> rem([4])
[]
>>> rem([4,4])
[4]
>>> rem([4, 1, 3, 2])
[]
>>> rem([2, 4, 2, 4, 4])
[2, 4, 4]

Answer 1

An easy implementation is to use collections.Counter:

def rem(iterable):
    c = collections.Counter(iterable)
    for k in c:
        c[k] -= 1
    return sorted(c.elements())

In Python versions before 2.7, collections.Counter is not available. You can use a set to record the items you already saw instead:

def rem(iterable):
   result = []
   seen = set()
   for x in iterable:
       if x in seen:
           result.append(x)
       else:
           seen.add(x)
   result.sort()
   return result