values = [200, 400, 50, -20, -100, 90, 780, -600]
n2z_one = [0 if v < 0 else v for v in values] # approach one
n2z_two = [v*(v>0) for v in values] #approach two

values: [200, 400, 50, -20, -100, 90, 780, -600]
n2z_one: [200, 400, 50, 0, 0, 90, 780, 0]
n2z_one: [200, 400, 50, 0, 0, 90, 780, 0]