Remove items from a list in Python based on previous items in the same list

Question

Say I have a simple list of numbers, e.g.

simple_list = range(100)

I would like to shorten this list such that the gaps between the values are greater than or equal to 5 for example, so it should look like

[0, 5, 10...]

FYI the actual list does not have regular increments but it is ordered

I'm trying to use list comprehension to do it but the below obviously returns an empty list:

simple_list2 = [x for x in simple_list if x-simple_list[max(0,x-1)] >= 5]

I could do it in a loop by appending to a list if the condition is met but I'm wondering specifically if there is a way to do it using list comprehension?

Answer 1

This is not a use case for a comprehension, you have to use a loop as there could be any amount of elements together that have less than five between them, you cannot just check the next or any n amount of numbers unless you knew the data had some very specific format:

simple_list = range(100)

def f(l):
    it = iter(l)
    i =  next(it)
    for ele in it:
        if abs(ele - i) >= 5:
            yield i
            i = ele
    yield i


simple_list[:] = f(simple_list)
print(simple_list)
[0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95]

A better example to use would be:

l = [1, 2, 2, 2, 3, 3, 3, 10, 12, 13, 13, 18, 24]

l[:] = f(l)

print(l)

Which would return:

[1, 10, 18, 24]

If your data is always in ascending order you can remove the abs and just if ele - i >= 5.