Original address

The error occurred during the execution of np.concatenate (, axis = 1) when

When I want to pile up two one-dimensional data, that is

# Pre
a = [1,2,3]
b = [4,5,6]
# New
[[1,2,3],
[4,5,6]]

use np.concatenate ((a,b),axis=1)

This is because both a and B are one-dimensional data with only one dimension, that is, axis = 0, and there is no axis = 1

I found two solutions

np.vstack ((A,B))

A and B can be stacked vertically

print(np.vstack((a,b)))	# Note that the parameter passed is '(a,b)'
# [[1 2 3] 
#  [4 5 6]]

The fly in the ointment is that this method can only pass two vectors to stack

np.newaxis + np.concatenate ()

Newaxis, as the name suggests, is a new axis. The usage is as follows

a = a[np.newaxis,:]	# Where ':' represents all dimensions (here 3), the shape of a becomes (1, 3), which is now two-dimensional
# [[1 2 3]]
b = b[np.newaxis,:]
# [[4 5 6]]

At this time, I can pile up two (1, 3) vectors into a matrix of (1 * 2, 3) = (2, 3). Note that axis = 0 should be used, that is, the first dimension

print(np.concatenate((a,b),axis=0))
# [[1 2 3] 
#  [4 5 6]]

relevant

Numpy: matrix merging