Adding n columns to a numpy array [duplicate]

Question

I'm making a program where I need to make a matrix looking like this:

A = np.array([[ 1.,  2.,  3.],
   [ 1.,  2.,  3.],
   [ 1.,  2.,  3.],
   [ 1.,  2.,  3.]])

So I started thinking about this np.arange(1,4)

But, how to append n columns of np.arange(1,4) to A?

Please include the complete code you've tried with np.arange — kdbanman
– kdbanman, Commented Nov 24, 2015 at 22:33
Do you want to append rows to A or create A that looks like the one in your question? For the latter case use numpy.repeat on axis=0. — Ashwini Chaudhary
– Ashwini Chaudhary, Commented Nov 24, 2015 at 22:35
Looks like he would like (4, 4, 4, 4) (5, 5, 5, 5), ... columns added to the array, but it's a bit vague... — Ricardo Cárdenes
– Ricardo Cárdenes, Commented Nov 24, 2015 at 22:36

Saeid · Accepted Answer · 2015-11-24 22:36:41Z

3

As mentioned in docs you can use concatenate

>>> a = np.array([[1, 2], [3, 4]])
>>> b = np.array([[5, 6]])
>>> np.concatenate((a, b), axis=0)
array([[1, 2],
       [3, 4],
       [5, 6]])
>>> np.concatenate((a, b.T), axis=1)
array([[1, 2, 5],
       [3, 4, 6]])

answered Nov 24, 2015 at 22:36

Saeid

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Comments

hpaulj · Accepted Answer · 2015-11-24 22:44:48Z

3

Here's another way, using broadcasting:

In [69]: np.arange(1,4)*np.ones((4,1))
Out[69]: 
array([[ 1.,  2.,  3.],
       [ 1.,  2.,  3.],
       [ 1.,  2.,  3.],
       [ 1.,  2.,  3.]])

answered Nov 24, 2015 at 22:44

hpaulj

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Comments

Frank M · Accepted Answer · 2015-11-24 22:39:34Z

1

You can get something like what you typed in your question with:

N = 3
A = np.tile(np.arange(1, N+1), (N, 1))

I'm assuming you want a square array?

answered Nov 24, 2015 at 22:39

Frank M

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John La Rooy · Accepted Answer · 2015-11-24 23:18:45Z

0

>>> np.repeat([np.arange(1, 4)], 4, 0)
array([[1, 2, 3],
       [1, 2, 3],
       [1, 2, 3],
       [1, 2, 3]])

answered Nov 24, 2015 at 23:18

John La Rooy

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