Numpy: quickest way to check if all elements in an array have the same sign?

Question

I'm looking for an optimized or cute way of checking if all the elements of an array have the same sign (strictly).

I've been thinking about doing:

N.all(my_array*my_array[0]>0)

as it would check if all the elements have the same sign as the first one, and so the same sign but it doesn't seem cute or elegant.

Answer 1

It seems like a waste to multiply the whole array. Just look at the sign of the first element and use that, I'd say:

N.all(my_array > 0) if my_array[0] > 0 else N.all(my_array < 0)

Answer 2

Try this:

len(N.unique(N.sign(a)))==1