Sorting of vector values

I have two vectors A and B obtained after MATLAB analysis. Both matrices have positive and negative values, starting from the same index. I want to replace all the negative values from let's say vector A with the corresponding positive values from vector B and vice-versa. How do I do that ?

[Paolo]

What happens when both A and B are negative at the same index?

[Guillaume]

And what happens if both are positive for that matter?

Why not take the maximum of both:

C = max(A, B);

[dpb]

"... what happens if both are positive...?"

As OP wrote the problem description, nothing happens to A as it's nonnegative.