how to stack numpy array in a list

Question

Say I have 3 numpy arrays: array([1, 2]), array([1, 2, 3]) and array([1, 2, 3, 4])

I want to get a list that look like [array([1, 2]), array([1, 2, 3]), array([1, 2, 3, 4])]

This can be done directly. However, I wonder how to get it done iteratively. Because if I start with L=[] and do

for i in range(3,6):
    L=[L, np.array(range(1,i))]

Then finally I will get a list of lists: [[[[], array([1, 2])], array([1, 2, 3])], array([1, 2, 3, 4])]. How can I get the desired result? Thanks.

The np.array(range(1,i)) is just an example. It can be any 1-D numpy array.

John1024 · Accepted Answer · 2014-09-11 01:23:52Z

1

L = []
for i in range(3,6):
    L.append(np.array(range(1,i)))

The creates:

[array([1, 2]), array([1, 2, 3]), array([1, 2, 3, 4])]

Alternatively, because L is a python list and not a numpy array:

L = []
for i in range(3,6):
    L = L + [np.array(range(1,i))]

answered Sep 11, 2014 at 1:23

John1024

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Comments

tom10 · Accepted Answer · 2014-09-11 01:30:06Z

0

What you are doing will work if you use append or +=, but you can also do this easily with the list comprehension:

[np.arange(1, i) for i in range(3,6)]

answered Sep 11, 2014 at 1:24

tom10

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