clean a list from doubles?? Help

Coding Python Support
1

I guys, i’m working on a script, but i’ve problem on removing double value in a list,

the list is formatted in this way: a = [(x,y),(k,j),…] ans so on,

the thing i want to do is to remove the repeated value starting from the end of the list, i want to do this because, virtually, each element have an index(a[i]) that i use for vertex so i’ can’t lost the the value at that index.

so i need to remove double from the end to the start of the list. there is a way to do this???

2

I think this should help:


for item in a:
    if a.count(item) >1:
        a.remove(item)

Downside is that the last occurance of the double value stays in the list and the first are deleted.

Otherwise you can create a new list


new_list = []


for item in a:
    if not item in new_list:
        new_list.append(item)

and work with the new list from then on

3

Hi rebellion,

Here’s the code I came up with;

seen = set()
add = seen.add
c = [i for i in a if ((i not in seen) and (add(i) is None))]

For those interested in how this works:

  • Create a set to store the unique objects which have been processed. Use a set because it has fast membership testing.
  • Store the method to add an object to the set.
  • For each element in a, if it hasn’t been seen before then add it to c and add it to the seen set.

Hope that helps.

Cheers,
Truman

4

or convert list to set and set to list

5

Hi PKHG,

That was my first thought too, however, converting a list to a set and back again does not maintain the order of the elements. If the order doesn’t matter then that way works fine.

Cheers,
Truman

6

hi guys, thanks for reply!! but sephiroth give me the inspiration, and i think i’ve solved the problem. the code of sephiroth, remove double , but if there are more then two repeat it dont see it, and it don’t remove from the end to the first.

so this is the code i used:

a.reverse()

    for item in a:

        while a.count(item) >1:
              a.remove(item)

   a.reverse()

the explanation:

a.reverse invert the list so i can remove the last element by first.
then i substitute “if” with “while” (it works i don’t know why ;P)

and then i reverse again the list