CODEWITHSUNDEEP
pythonarraysnumpy
user3243499
user3243499

Reputation: 3151

How to append a last column (1d array) to a 2d numpy array in python?

I have two arrays:

import numpy as np
a = np.array([[1,2,3], [4,5,6]])
b = np.array([5, 6])

when I try to append b to a as a's last column using the below code

 np.hstack([a, b])



it thows an error:
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<__array_function__ internals>", line 6, in hstack
  File "C:\Users\utkal\anaconda3\envs\AIML\lib\site-packages\numpy\core\shape_base.py", line 345, in hstack
    return _nx.concatenate(arrs, 1)
  File "<__array_function__ internals>", line 6, in concatenate
ValueError: all the input arrays must have same number of dimensions, but the array at index 0 has 2 dimension(s) and the array at index 1 has 1 dimension(s)

I want the final array as:

1 2 3 5
4 5 6 6

Upvotes: 0

Views: 1555

Answers (2)

Andy L.
Andy L.

Reputation: 25239

np.hstack is a shortcut for np.concatenate on axis=1. So, it requires both arrays have the same shapes with all dimensions matching except on concatenate axis. In your case, you need both array in 2-d and matching on dimension 0

So you need

np.hstack([a, b[:,None]])

Out[602]:
array([[1, 2, 3, 5],
       [4, 5, 6, 6]])

Or use np.concatenate

np.concatenate([a, b[:,None]], axis=1)

Out[603]:
array([[1, 2, 3, 5],
       [4, 5, 6, 6]])

Upvotes: 1

flabons
flabons

Reputation: 331

You can do it like this:

np.hstack((a,b.reshape(2,1)))
array([[1, 2, 3, 5],
       [4, 5, 6, 6]])

Upvotes: 3

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