Question

Sorry for the poorly worded title but I asked a question earlier about getting a unique list of items from two lists. People told me to make the list -> sets and then union.

So now I’m wondering if it’s faster to:

1. While adding one item to a list, scan the whole list for duplicates.
2. Make that one item a set and then union sets.

I should probably just read up on sets in hindsight…

In Python, by the way – sorry for not clarifying.

Answer 1

as you can see extending one list by another end then remove duplicates by making set
is the fastest way(at least in python;))

>>> def foo():
...     """
...     extending one list by another end then remove duplicates by making set
...     """
...     l1 = range(200)
...     l2 = range(150, 250)
...     l1.extend(l2)
...     set(l1)
... 
>>> def bar():
...     """
...     checking if element is on one list end adding it only if not
...     """
...     l1 = range(200)
...     l2 = range(150, 250)
...     for elem in l2:
...             if elem not in l1:
...                     l1.append(elem)
... 
>>> def baz():
...     """
...     making sets from both lists and then union from them
...     """
...     l1 = range(200)
...     l2 = range(150, 250)
...     set(l1) | set(l2)
... 
>>> from timeit import Timer
>>> Timer(foo).timeit(10000)
0.265153169631958
>>> Timer(bar).timeit(10000)
7.921358108520508
>>> Timer(baz).timeit(10000)
0.3845551013946533
>>>