Transforming a row vector into a column vector in Numpy

Question

Let\'s say I have a row vector of the shape (1, 256). I want to transform it into a column vector of the shape (256, 1) instead. How would you do it in Numpy?

Answer 1

To convert a row vector into a column vector in Python can be important e.g. to use broadcasting:

import numpy as np

def colvec(rowvec):
    v = np.asarray(rowvec)
    return v.reshape(v.size,1)

colvec([1,2,3]) * [[1,2,3], [4,5,6], [7,8,9]]

Multiplies the first row by 1, the second row by 2 and the third row by 3:

array([[ 1,  2,  3],
       [ 8, 10, 12],
       [  21, 24, 27]])

In contrast, trying to use a column vector typed as matrix:

np.asmatrix([1, 2, 3]).transpose() * [[1,2,3], [4,5,6], [7,8,9]]

fails with error ValueError: shapes (3,1) and (3,3) not aligned: 1 (dim 1) != 3 (dim 0).