Dividing a list of arrays to a smaller list of arrays

November 21, 2021

In my current research project, I have a list of arrays similar to the one shown bellow:

import numpy as np
[np.array([ 0.00727845,  0.00363923, -0.00976286, -0.00488143]),
 np.array([ 0.00493276,  0.00246638, -0.00893927, -0.00446964]),
 np.array([ 0.00283457,  0.00141729, -0.00780608, -0.00390304]),
 np.array([ 0.00104456,  0.00052228, -0.00649412, -0.00324706]),
 np.array([-0.00040696, -0.00020348, -0.00511511, -0.00255755]),
 np.array([-0.00151502, -0.00075751, -0.00375973, -0.00187987])]

Here, the length of each individual array is the same. let it e N
Then I need to separate each array in to half and collect them separately.

That is:

list_1 = 
[np.array([ 0.00727845,  0.00363923, ]),
 np.array([ 0.00493276,  0.00246638, ]),
 np.array([ 0.00283457,  0.00141729, ]),
 np.array([ 0.00104456,  0.00052228, ]),
 np.array([-0.00040696, -0.00020348, ]),
 array([-0.00151502, -0.00075751, ])]

list_2 =
np.array([ -0.00976286, -0.00488143]),
 np.array([ -0.00893927, -0.00446964]),
 np.array([-0.00780608, -0.00390304]),
 np.array([  -0.00649412, -0.00324706]),
 np.array([ -0.00511511, -0.00255755]),
 array([ -0.00375973, -0.00187987])]

I can think of a very lengthy method using for loops to do this but I suppose there is a better way of handling. Appreciate your help

>Solution :

We could use a list comprehension approach here:

import numpy as np

inp = [
    np.array([ 0.00727845,  0.00363923, -0.00976286, -0.00488143]),
    np.array([ 0.00493276,  0.00246638, -0.00893927, -0.00446964]),
    np.array([ 0.00283457,  0.00141729, -0.00780608, -0.00390304]),
    np.array([ 0.00104456,  0.00052228, -0.00649412, -0.00324706]),
    np.array([-0.00040696, -0.00020348, -0.00511511, -0.00255755]),
    np.array([-0.00151502, -0.00075751, -0.00375973, -0.00187987])
]
list_1 = [np.array(x[0:2]) for x in inp]
list_2 = [np.array(x[2:4]) for x in inp]
print(list_1)

This prints:

 [array([0.00727845, 0.00363923]),
  array([0.00493276, 0.00246638]),
  array([0.00283457, 0.00141729]),
  array([0.00104456, 0.00052228]),
  array([-0.00040696, -0.00020348]),
  array([-0.00151502, -0.00075751])]