How to return 1 or -1 if number is positive or negative (including 0)?

Question

Can I ask how to achieve this in Python:

Input: I = [10,-22,0]

Output: O = [1,-1,-1]

I was thinking O=I/abs(I)

But how to deal with zero?

Answer 1

The following should do what you want:

>>> I = [10,-22,0]
>>> O = [1 if v > 0 else -1 for v in I]
>>> O
[1, -1, -1]
>>> 

If you want to use map with a lambda , you can do:

>>> O = map(lambda v: 1 if v > 0 else -1, I)
>>> O
[1, -1, -1]
>>> 

Answer 2

You can just do this:

I = [10,-22,0]
output = []

for num in I:
    if num <=0:
        output.append(-1)
    else:
        output.append(1)

print output