Combining list of 2D numpy arrays

Question

How do I combine N, 2D numpy arrays (of dimension R x C) to create a 3D numpy array of shape (N, R, C)? Right now, the N-2D numpy arrays are contained inside a list, and I want that to become a 3D numpy array. Let's say X is my list of 2D numpy arrays, if I just do np.array(X), I get something of shape (N,). If I do np.vstack(X), I get something of shape (N x R, C). How do I solve this problem?

If np.array(X) does not give you a 3d array, I suspect one of more of the 2d arrays differs in size. You might try np.stack(X), but it too expects the shapes to match. If they just differ in the R shape, vstack should work, but the N*R dimension is doubtful. You could though reshape the vstack result. — hpaulj
– hpaulj, Commented Jun 6, 2019 at 23:55
Thanks the issue was indeed that. Once I fixed that issue, I was good. — Jane Sully
– Jane Sully, Commented Jun 7, 2019 at 0:05

remeus · Accepted Answer · 2019-06-06 23:36:29Z

0

You can use np.stack:

test = np.stack([np.ones([2, 3]) for _ in range(4)]) 
print(test.shape) # (4, 2, 3)

answered Jun 6, 2019 at 23:36

remeus

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Ayoub ZAROU · Accepted Answer · 2019-06-06 23:45:02Z

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you could just use :

np.array([np.array(x) for x in ArrayList])

edited Jun 6, 2019 at 23:45

answered Jun 6, 2019 at 23:39

Ayoub ZAROU

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1 Comment

Code-Apprentice Over a year ago

If 2DarrayList is already a list of numpy arrays, you don't need the list comp. Note: 2DarrayList is not a valid variable name

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