Remove items from list by using python list comprehensions

Question

I have a list of integers which goes like this:

unculledlist = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29]

I would like cull the values from this list, so that it looks like this:

culledlist = [0, 2, 4, 10, 12, 14, 20, 22, 24]

But I would like to do this by using list comprehensions.

This is a graphical preview of how I am trying to cull the list values. It's easier to understand if I arrange the list values into rows and columns. But this is only visually. I do not need nested lists:

I can do it by using two nested loops:

unculledlist = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29]

index = 0
culledlist = []
for i in range(6):
    for j in range(5):
        if (i % 2 == 0) and (j % 2 == 0):
            culledlist.append(unculledlist[index])
        index += 1

print "culledlist: ", culledlist  # culledlist = [0, 2, 4, 10, 12, 14, 20, 22, 24]

But I would like to do it with python list comprehensions instead.

Can anyone provide an example please?

Thank you.

EDIT:

The reason why I would like to use list comprehensions is because my actual unculledlist has a couple of million of integers. Solving this issue with list comprehensions will definitively speed things up. I do not care about readability. I just want to make a quicker solution.

I can not use numpy nor scipy modules. But I can use itertools module. Not sure if solution with itertools would be quicker than the one with list comprehensions? Or even lambda?

Answer 1

I saw this and thought string manipulation would be the easier approach

culled_list = [item for item in unculledlist if str(item)[-1] in ['0','2','4']]

The result is still a list of integers

>>> culled_list
[0, 2, 4, 10, 12, 14, 20, 22, 24]

Thanks to eugene y for the less complicated approach

>>> culled_list = [item for item in unculledlist if item % 10 in (0,2,4)]
>>> culled_list
[0, 2, 4, 10, 12, 14, 20, 22, 24]

Answer 2

You can do it with a list comprehension like this:

[x for i, x in enumerate(unculledlist) if (i % 6) % 2 == 0 if (i % 5) % 2 == 0]

The output is:

[0, 2, 4, 10, 12, 14, 20, 22, 24]

Answer 3

You could read the list in 5-items chunks and extract elements with even indexes from every even chunk:

>>> [x for i, v in enumerate(range(0, len(unculledlist), 5)) if not v % 2 for x in unculledlist[v:v+5:2]]
[0, 2, 4, 10, 12, 14, 20, 22, 24]