Python Calculation Using List

Question

How can I perform calculations in python using two lists? Where the first calculation would be, c = -(1)/cos(4), second being, c = -(5)/cos(6), etc

import numpy as np
x, y = [1,5,2,1], [4,6,2,3]
c = []
c = -x/(np.cos(y))
print(c)

When I try this I currently get the error :

TypeError: bad operand type for unary -: 'list' 

• juanpa.arrivillaga: why are you trying to use lists like numpy arrays?
• pasbi: To me, it's not clear what you're asking. Do you want to use list like a numpy-array? (if so, why avoid numpy?) Or do you want to learn how to use numpy arrays?

Answer 1

This can be done without numpy:

from math import cos
x, y = [1,5,2,1], [4,6,2,3]
c = [-i/cos(j) for i,j in zip(x,y)]

Answer 2

You have to cast the list to numpy array.

c = -np.array(x)/(np.cos(y))
print(c)

now you will have the results store in the np array

array([ 1.52988566, -5.20740963, 4.80599592, 1.01010867])

or if you want a list again

c = list(c)

Answer 3

You can iterate over the length of the list:

import numpy as np
x, y = [1,5,2,1], [4,6,2,3]
c = []
for i in range(0, len(x)):
 f = -x[i]/(np.cos(y[i]))
 c.append(f)
print(c)

Answer 4

Hope ... there is no specific reason ... to handle as a list.

import numpy as np
x, y = [1,5,2,1],[4,6,2,3]
c = []
for k in range (len(x)):
 c = -x[k]/(np.cos(y[k]))
 print(c)
Result:
1.5298856564663974
-5.207409632975539
4.805995923444762
1.0101086659079939

Answer 5

The error tells you the problem: TypeError: bad operand type for unary -: 'list'

So you could just negate elsewhere (where you have a NumPy array):

c = -x/np.cos(y) # Error
c = x/-np.cos(y) # [ 1.52988566 -5.20740963 4.80599592 1.01010867]
c = -(x/np.cos(y)) # [ 1.52988566 -5.20740963 4.80599592 1.01010867]