CODEWITHSUNDEEP
pythonlist
zemone
zemone

Reputation: 97

How to multiply two lists of floats

I have two lists: Dir and Vel. Each item in each list is a float (list of floats). So 1500 elements in Vir (a list), whereby each element is a float. Same for Dir. Values are both NaNs and then real numbers like 1, 1.5, 2, 2.5, etc. I am trying to compute u = Vel * sin(radians(Dir)). In Matlab it would be simply Vel .* sin(radians(Dir)).

Dir and Vel are both type list. When I open the list, there are 1500 elements of type float. I have tried float(Dir) without any luck. I have math and numpy installed. My specific code is: 

u = [a * b for a, b in zip(Vel,sin(radians(Dir)))]

I am trying to compute the u and v vector shown above but I keep getting the error that a float is required - even though each list contains only floats. What am I doing wrong?

Upvotes: 0

Views: 1053

Answers (2)

Norrius
Norrius

Reputation: 7920

You are probably trying to apply the standard math.sin and math.radians to an iterable, which is not going to work (they require a scalar). Luckily, NumPy supports vector operations:

import numpy as np

vel = np.array([3., 10., 40.])
dir = np.array([30., 0., 90.])

u = vel * np.sin(np.radians(dir))  # element-wise multiplication
print(u)  # prints [ 1.5  0.  40. ]

Upvotes: 2

Kevin Welch
Kevin Welch

Reputation: 1508

The problem is that you are doing sin(radians(Dir)) when Dir is a list. Try doing the math on a and b instead.

[v*(sin(radians(d))) for v,d in zip(vel, dir)]

Upvotes: 1

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