Python List of np arrays to array

Question

I'm trying to turn a list of 2d numpy arrays into a 2d numpy array. For example,

dat_list = []
for i in range(10):
    dat_list.append(np.zeros([5, 10]))

What I would like to get out of this list is an array that is (50, 10). However, when I try the following, I get a (10,5,10) array.

output = np.array(dat_list)

Thoughts?

wim · Accepted Answer · 2019-11-07 20:00:21Z

95

you want to stack them:

np.vstack(dat_list)

edited Nov 7, 2019 at 20:00

answered Aug 26, 2011 at 6:37

wim

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1 Comment

Good Fit Over a year ago

For list of arrays with different shapes, one should use: np.concatenate(list, axis=None)

Anand · Accepted Answer · 2020-11-19 02:45:53Z

3

Above accepted answer is correct for 2D arrays as you requested. For 3D input arrays though, vstack() will give you a surprising outcome. For those, use stack(<list of 3D arrays>, 0).

answered Nov 19, 2020 at 2:45

Anand

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Comments

Messypuddle · Accepted Answer · 2019-07-22 15:15:14Z

1

See https://docs.scipy.org/doc/numpy/reference/generated/numpy.append.html for details. You can use append, but will want to specify the axis on which to append.

dat_list.append(np.zeros([5, 10]),axis=0)

answered Jul 22, 2019 at 15:15

Messypuddle

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