Appending multiple arrays into a list in Python

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I have two arrays A1 and A2 with shapes (1,3) and (1,4) respectively. I want to append these two arrays into a list. I present the expected output.

import numpy as np
A1=np.array([[128, 129, 131]])
A2=np.array([[128, 131, 132, 140]])

The expected output is

A=[array([[128, 129, 131]]), array([[128, 131, 132, 140]])]
list numpy python
1 Answers

As numpy allows fast numerical manipulations it expects all the arrays to be of the same shape, so in your case (i.e., A1.shape = 3 and A2.shape = 4) you won't be able to convert the combined array into numpy. The only thing you can do is to use the python list object, as pointed by @hapulj by:

C = [A1, A2]

but it certainty be slower than using numpy due to the header appended by python to represent the objects in the list (more on that here), so I'd recommend making sure your arrays are of the same length (e.g., by adding 0 if it make sense in your case), and then using something like:

import numpy as np
A1=np.array([[128, 129, 131, 0]])
A2=np.array([[128, 131, 132, 140]])

C  = np.array([A1, A2], dtype=np.int16)

Output:

array([[[128, 129, 131,   0]],

       [[128, 131, 132, 140]]], dtype=int16)

Cheers

user_45960780
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