# np.hstack concatenates arrays column-wise
a = np.array([1], [2], [3]) #read as a vector, i.e. a column
b = np.array([4], [5], [6]) #read as a vector, i.e. a column
#concatenated to the first one
c = np.hstack((a, b)))
print(c)
# output is
# [[1, 4],
# [2, 5],
# [3, 6]]
