How to make a list of 2D 3x3 array and save the ndarray with numpy save?

Question

So let's say I have some 3x3 matrix I get with a calculation I am doing, let's say

np.array([[1,2,3],[4,5,6],[7,8,9]])

np.array([[0,0,0],[0,0,0],[0,0,0]])

I want to add this onto some matrix A and be able to access them so that if I do

> A[0]
> [[1,2,3],[4,5,6],[7,8,9]]
> A[1]
> [[0,0,0],[0,0,0],[0,0,0]]

and keep adding on bunch of these 2D array and save them with np.save('A', A) for fast access later. I kind of saw it is possible with appending to a list but I can't save a list with np.save for fast efficient access. How can I create a empty ndarray I can add matrix onto and save it all as .npy?

HHYurdagul · Accepted Answer · 2020-07-01 23:16:19Z

1

You can convert list to array it is the same:

A = list()
A.append(x)
A.append(y)
X = np.array(A)
np.save('X', X)

answered Jul 1, 2020 at 23:16

HHYurdagul

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Ehsan · Accepted Answer · 2020-07-02 05:19:44Z

0

Originally use this:

A = np.stack((a,b))
[[[1 2 3]
  [4 5 6]
  [7 8 9]]

 [[0 0 0]
  [0 0 0]
  [0 0 0]]]

And once you have formed A, if you want to add another array c to A use:

A = np.vstack((A,[c]))

output for c=a:

[[[1 2 3]
  [4 5 6]
  [7 8 9]]

 [[0 0 0]
  [0 0 0]
  [0 0 0]]

 [[1 2 3]
  [4 5 6]
  [7 8 9]]]

answered Jul 2, 2020 at 5:19

Ehsan

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