extracting numbers from list

Question

I've created a list (which is sorted):

indexlist = [0, 7, 8, 12, 19, 25, 26, 27, 29, 30, 31, 33]

I want to extract the numbers from this list that are at least five away from each other and input them into another list. This is kind of confusing. This is an example of how I want the output:

outlist = [0, 7, 19, 25, 31]

As you can see, none of the numbers are within 5 of each other.

I've tried this method:

for index2 in range(0, len(indexlist) - 1):
        if indexlist[index2 + 1] > indexlist[index2] + 5:
            outlist.append(indexlist[index2])

However, this gives me this output:

outlist = [0, 12, 19]

Sure, the numbers are at least 5 away, however, I'm missing some needed values.

Any ideas about how I can accomplish this task?

Answer 1

You need to keep track of the last item you added to the list, not just compare to the following value:

In [1]: indexlist = [0, 7, 8, 12, 19, 25, 26, 27, 29, 30, 31, 33]
In [2]: last = -1000 # starting value hopefully low enough :)
In [3]: resultlist = []
In [4]: for item in indexlist:
   ...:     if item > last+5:
   ...:         resultlist.append(item)
   ...:         last = item
   ...:
In [5]: resultlist
Out[5]: [0, 7, 19, 25, 31]

Answer 2

This should do the trick. Here, as I said in comment, the outlist is initialised with the first value of indexlistand iterated indexlist elements are compared to it. It is a rough solution. But works.

indexlist = [0, 7, 8, 12, 19, 25, 26, 27, 29, 30, 31, 33]
outlist = [indexlist[0]]

for index2 in range(1, len(indexlist) - 1):
        if indexlist[index2] > (outlist[-1] + 5):
            outlist.append(indexlist[index2])

output:

>>outlist

[0, 7, 19, 25, 31]