Creating arrays from lists

5.2.3. Creating arrays from lists#

A simple way to create an array from a list is to use the np.array function. To create the unidimensional array of Fig. 5.2, we would write:

Fig. 5.2 A unidimensional array.#

import numpy as np

array_1d = np.array([0.0, 0.1, 0.2, 0.3])

array_1d
array([0. , 0.1, 0.2, 0.3])

It is also possible to convert back an array to a list, using its tolist method:

array_1d.tolist()
[0.0, 0.1, 0.2, 0.3]

To create the bidimensional array of Fig. 5.3, we would use nested lists:

Fig. 5.3 A bidimensional array.#

array_2d = np.array(
    [
        [0.0, 0.1, 0.2, 0.3],
        [0.4, 0.5, 0.6, 0.7],
        [0.8, 0.9, 1.0, 1.1],
    ]
)

array_2d
array([[0. , 0.1, 0.2, 0.3],
       [0.4, 0.5, 0.6, 0.7],
       [0.8, 0.9, 1. , 1.1]])

To create the tridimensional array of Fig. 5.4, we would use multiple levels of nested lists:

Fig. 5.4 A tridimensional array.#

array_3d = np.array(
    [
        [
            [0.0, 0.1, 0.2, 0.3],
            [0.4, 0.5, 0.6, 0.7],
            [0.8, 0.9, 1.0, 1.1],
        ],
        [
            [1.2, 1.3, 1.4, 1.5],
            [1.6, 1.7, 1.8, 1.9],
            [2.0, 2.1, 2.2, 2.3],
        ],
        [
            [2.4, 2.5, 2.6, 2.7],
            [2.8, 2.9, 3.0, 3.1],
            [3.2, 3.3, 3.4, 3.5],
        ],
    ]
)

array_3d
array([[[0. , 0.1, 0.2, 0.3],
        [0.4, 0.5, 0.6, 0.7],
        [0.8, 0.9, 1. , 1.1]],

       [[1.2, 1.3, 1.4, 1.5],
        [1.6, 1.7, 1.8, 1.9],
        [2. , 2.1, 2.2, 2.3]],

       [[2.4, 2.5, 2.6, 2.7],
        [2.8, 2.9, 3. , 3.1],
        [3.2, 3.3, 3.4, 3.5]]])