Concatenation of 2 1D `numpy` Arrays Along 2nd Axis

Question

Executing

import numpy as np
t1 = np.arange(1,10)
t2 = np.arange(11,20)

t3 = np.concatenate((t1,t2),axis=1)

results in a

Trac         


        

Answer 1

This is because of Numpy's way of representing 1D arrays. The following using reshape() will work:

t3 = np.concatenate((t1.reshape(-1,1),t2.reshape(-1,1),axis=1)

Explanation: This is the shape of the 1D array when initially created:

t1 = np.arange(1,10)
t1.shape
>>(9,)

'np.concatenate' and many other functions don't like the missing dimension. Reshape does the following:

t1.reshape(-1,1).shape
>>(9,1)