Python: Appending an array like in MATLAB

Question

How do I initialize and append an array like in MATLAB

for i = 1:10
    myMat(i,:) = [1,2,3]
end

Thanks.

Answer 1

You should look into numpy if you want an object similar to MATLAB's array constructs. There are many ways to construct arrays using numpy, but it sounds like you might be interested in joining or appending.

However, the strictest way to do what the MATLAB code in your question is doing is to construct the array first, then assign to it by slice:

import numpy as np

mat = np.empty((10, 3))
for idx in range(10):
    mat[idx, :] = [1, 2, 3]

print(mat)

This will output

[[ 1.  2.  3.]
 [ 1.  2.  3.]
 [ 1.  2.  3.]
 [ 1.  2.  3.]
 [ 1.  2.  3.]
 [ 1.  2.  3.]
 [ 1.  2.  3.]
 [ 1.  2.  3.]
 [ 1.  2.  3.]
 [ 1.  2.  3.]]

Answer 2

Here is one approach:

In [18]: import numpy as np

In [19]: a = np.empty((10, 3))

In [20]: a[:] = np.array([1,2,3])

In [21]: a
Out[21]:
array([[ 1.,  2.,  3.],
       [ 1.,  2.,  3.],
       [ 1.,  2.,  3.],
       [ 1.,  2.,  3.],
       [ 1.,  2.,  3.],
       [ 1.,  2.,  3.],
       [ 1.,  2.,  3.],
       [ 1.,  2.,  3.],
       [ 1.,  2.,  3.],
       [ 1.,  2.,  3.]])