Two lists in python. Check when the elements are of the same sign

Question

I have two lists in python

list1=[1,3,5,-3,-3]
list2=[2,-3,3,-3,5]

I want to produce a list that is true when the elements are of the same sign

result=[True,False,True,True,False]

which is the fastest and more pythonic way to do this?

EDIT:

Solution

I solve it by transforming both list to numpy arrays

np.array(list1)*np.array(list1)>0

Also, what is expected result when at least one of the elements is zero. — buran, Dec 29 '22 at 09:08
m m m that turns complicated. if 0 i would like that it produces false for any other number negative or positive — KansaiRobot, Dec 29 '22 at 09:23

score 2 · Answer 1 · answered Dec 29 '22 at 09:06

2

The product of two numbers of the same sign should be positive, so you can do:

result = [a * b > 0 for a, b in zip(list1, list2)]

answered Dec 29 '22 at 09:06

blhsing

"should be"? Are there some circumstances where that might not be the case? Also, if a pair of values are both zero this would give False so I suppose that depends on whether or not zero can be considered to be signed. – DarkKnight Dec 29 '22 at 09:09
@Fred Well, floats can overflow and produce `inf`s. – Lodinn Dec 29 '22 at 09:15
mm yes i was thinking of that but this implies the use of for. isn't that slow ? – KansaiRobot Dec 29 '22 at 09:20
i wonder if this https://stackoverflow.com/a/10271498/4451521 is better? – KansaiRobot Dec 29 '22 at 09:33

1 Answers1