[Tutor] Uniques values in a list

[Alexandre Ratti]

Hi Sean,


At 07:45 16/03/2002 -0800, Sean 'Shaleh' Perry wrote:
[Filtering out unique values from a list:]
> > => Do you know any other solution (eg. using functional programming or
> > similar woodoo)?
>
>the "standard" approach is to sort the list, then walk it.  You hold the first
>index in your hand and look at the second.  If they match you dump the 
>second and move on to the third.  You continue until a non-match is 
>found.  you then hold the new item and look at the next one.

Thanks for this information. I guess this is the approach described in the 
Python FAQ. Here is an example (slighty modified):

def filterList(theList):
     if theList:
         theList.sort()
         last = theList[-1]
         for i in range(len(theList) - 2, -1, -1):
             if last == theList[i]:
                 del theList[i]
             else:
                 last = theList[i]
     return theList


if __name__ == "__main__":
     toto = [1, 2, 2, 3, 4, 5, 3, 2, 7]
     print filterList(toto)

 >>> [1, 2, 3, 4, 5, 7]

>This is from the g++ 3.0 stl.
>
>void list::unique
>{
>   iterator __first = begin();
>   iterator __last = end();
>   if (__first == __last) return;
>   iterator __next = __first;
>   while (++__next != __last) {
>     if (*__first == *__next)
>       erase(__next);
>     else
>       __first = __next;
>     __next = __first;
>   }
>}

One difference is that the Python example does a reverse loop, whereas your 
code snippet loops from first to last, if I understand it correctly.


Cheers.

Alexandre