Some more facts from the numpy docs :
With syntax as numpy.concatenate((a1, a2, ...), axis=0, out=None)
axis = 0 for row-wise concatenation axis = 1 for column-wise concatenation
>>> a = np.array([[1, 2], [3, 4]])
>>> b = np.array([[5, 6]])
# Appending below last row
>>> np.concatenate((a, b), axis=0)
array([[1, 2],
[3, 4],
[5, 6]])
# Appending after last column
>>> np.concatenate((a, b.T), axis=1) # Notice the transpose
array([[1, 2, 5],
[3, 4, 6]])
# Flattening the final array
>>> np.concatenate((a, b), axis=None)
array([1, 2, 3, 4, 5, 6])
I hope it helps !