How to add dimension to a python numpy array

Question

Let's suppose i have this array:

import numpy as np
x = np.arange(4)

array([0, 1, 2, 3])

I want to write a very basic formula which will generate from x this array:

array([[0, 1, 2, 3],
       [1, 2, 3, 4],
       [2, 3, 4, 5],
       [3, 4, 5, 6]])

What is the shortest way to do that with python and numpy ?

Thanks

Not sure it's a dupe of that, @Divakar. Looks like he may want x[None, :] + x[:, None] Which is probably a dupe of something else, simple as it is. — Daniel F
– Daniel F, Commented May 10, 2017 at 9:26
Not from the original x array he specified. There are no 4,5,6 elements to stride to using stride_tricks — Daniel F
– Daniel F, Commented May 10, 2017 at 9:29

Allen Qin · Accepted Answer · 2017-05-10 13:11:18Z

1

The easiest way I can think of is to use numpy broadcasting.

x[:,None]+x
Out[87]: 
array([[0, 1, 2, 3],
       [1, 2, 3, 4],
       [2, 3, 4, 5],
       [3, 4, 5, 6]])

answered May 10, 2017 at 13:11

Allen Qin

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Comments

Tom de Geus · Accepted Answer · 2017-05-10 12:39:37Z

0

This should do what you want (note that I have introduced a different number of rows (5) than of columns (4) to make a clear distinction):

import numpy as np

A = np.tile(np.arange(4).reshape(1,4),(5,1))+np.tile(np.arange(5).reshape(5,1),(1,4))

print(A)

A break-down of steps:

The sum of the two results in what you want:

[[0 1 2 3]
 [1 2 3 4]
 [2 3 4 5]
 [3 4 5 6]
 [4 5 6 7]]

answered May 10, 2017 at 12:39

Tom de Geus

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