Python: create an empty Numpy array/matrix

Question

How to create an empty matrix so that I can update its cells using index values.

E.g.

[[0, 0, 0],

 [0, 0, 0],

 [0, 0, 0]]

 

Answer 1

You can use Numpy's empty() or zeros() or ones() to declare an array or matrix of any size. empty() will put some random numbers in cells, zeros() will put 0 and ones() will put 1.

>>> import numpy as np
>>> aa=np.zeros((3,3), dtype=int)
>>> aa
array([[0, 0, 0],
       [0, 0, 0],
       [0, 0, 0]])
>>> aa[2][2]=5
>>> aa
array([[0, 0, 0],
       [0, 0, 0],
       [0, 0, 5]])

>>> bb=np.empty((3,3), dtype=int)
>>> bb
array([[       19609920,        20491424, 140256443196784],
       [140256732807088, 140256808845232, 140256808299056],
       [140256808398384, 140256807864816,              80]])
>>> cc=np.ones((3,3), dtype=int)
>>> cc
array([[1, 1, 1],
       [1, 1, 1],
       [1, 1, 1]])
>>> bb[1][0]=0
>>> bb
array([[       19609920,        20491424, 140256443196784],
       [              0, 140256808845232, 140256808299056],
       [140256808398384, 140256807864816,              80]])
>>> cc[2][0]=5
>>> cc
array([[1, 1, 1],
       [1, 1, 1],
       [5, 1, 1]])
>>>

>>> dd=np.ones((3,3,3), dtype=int)
>>> dd
array([[[1, 1, 1],
        [1, 1, 1],
        [1, 1, 1]],

       [[1, 1, 1],
        [1, 1, 1],
        [1, 1, 1]],

       [[1, 1, 1],
        [1, 1, 1],
        [1, 1, 1]]])

>>> ee=np.ones((3), dtype=int)
>>> ee
array([1, 1, 1])