3

Hi so I'm trying to figure out how to create an iterator object using Python that would remove duplicates or more so omit duplicates.

For example I have a list (1, 2, 3, 3, 4, 4, 5) and I get (1, 2, 3, 4, 5)

I understand that in order to get an iterator object I have to create it. So:

Class Unique:
    def __init__(self, n):
         self.i = 0
         self.n = n  

    def __iter__(self):
         return self

    def __next__(self):
        if self.i < self.n:

I'm actually not entirely sure what to do next in this problem. Thanks in advance for any comments or help!

d'chang
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  • Why create a new class instead of using a `set` or subclassing `set`? – Deacon Aug 14 '15 at 15:00
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    It more of an exercise to implement using Iterator objects (for a quiz in my class) and it helps to understand how iterators work. I understand using 'set' as a built-in function but if someone could please help me in writing this it would be greatly appreciated. – d'chang Aug 14 '15 at 15:02

3 Answers3

8

Better create a generator function, like this

>>> def unique_values(iterable):
...     seen = set()
...     for item in iterable:
...         if item not in seen:
...             seen.add(item)
...             yield item
...

And then you can create a tuple of unique values, like this

>>> tuple(unique_values((1, 2, 3, 3, 4, 4, 5)))
(1, 2, 3, 4, 5)

If you know for sure that the data will be always sorted, then you can avoid creating the set and keep track of the previous data only, like this

>>> def unique_values(iterable):
...     it = iter(iterable)
...     previous = next(it)
...     yield previous
...     for item in it:
...         if item != previous:
...             previous = item
...             yield item
>>> tuple(unique_values((1, 2, 3, 3, 4, 4, 5)))
(1, 2, 3, 4, 5)

You can write an iterator object, with a class, like this

>>> class Unique:
...     def __init__(self, iterable):
...         self.__it = iter(iterable)
...         self.__seen = set()
... 
...     def __iter__(self):
...         return self
... 
...     def __next__(self):
...         while True:
...             next_item = next(self.__it)
...             if next_item not in self.__seen:
...                 self.__seen.add(next_item)
...                 return next_item
... 
>>> for item in Unique((1, 2, 3, 3, 4, 4, 5)):
...     print(item)
... 
1
2
3
4
5

You can refer this answer, and the Iterator Types section in Python 3 Data Model documentation

Community
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thefourtheye
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    I understand how to create the generator function but I was wondering how to create an iterator object for the same method. I'm reviewing for a test so it would be really helpful! – d'chang Aug 14 '15 at 14:53
  • Keep in mind this assumes the items in `iterable` are hashable (so that they can be added to the set). – chepner Aug 14 '15 at 14:54
  • @thefourtheye Thanks that makes a lot of sense and thanks for the refer answer! – d'chang Aug 14 '15 at 15:04
0

If preserving original order is not important, simply use set: 

values = (1, 3, 2, 5, 4, 3)
unique_values = set(values)
print unique_values
(1, 2, 3, 4, 5)
Jimothy
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0

This should remove all duplicates

new_stuff = type(old_stuff)(set(old_stuff))
Toothpick Anemone
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