How to add numpy array variables by index without using loops

Question

I have this problem where I would prefer not using loops because I am working with a big data as a solution :

This is what I am trying to do : (I know this works to [6 6 6], but I want to "join" it by index)

import numpy as np

np_1 = np.asarray([1,1,1])
np_2 = np.asarray([2,2,2])
np_3 = np.asarray([3,3,3])

np_4 = np_1 + np_2 + np_3
# np_4 should be [1,2,3,1,2,3,1,2,3]

Are there ways to do this? or should I look for options outside of numpy?

what you're trying to do is array stacking - see the numpy docs guide how to create an array from existing data — Michael Delgado
– Michael Delgado, Commented Aug 5, 2022 at 3:14
Does this answer your question? How to properly stack numpy arrays? — Michael Delgado
– Michael Delgado, Commented Aug 5, 2022 at 3:14

Ralph Tandetzky · Accepted Answer · 2022-08-05 05:59:51Z

0

Try this:

np.array([np_1, np_2, np_3]).transpose().flatten()

answered Aug 5, 2022 at 5:59

Ralph Tandetzky

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mr.curiousity · Accepted Answer · 2022-08-05 03:45:15Z

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You can try the following method:

np.ravel(np.stack(np_1,np_2,np3),'F')

answered Aug 5, 2022 at 3:45

mr.curiousity

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1 Comment

Mark Over a year ago

I think you are missing a set of brackets. This is a TypeError as currently posted. Also the typo: np3 -> np_3.

Aaron Lei · Accepted Answer · 2022-08-05 05:15:17Z

0

One way to do it is to stack the sequences depth-wise and flatten it:

np.dstack([np_1, np_2, np_3]).flatten()

answered Aug 5, 2022 at 5:15

Aaron Lei

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