[Numpy-discussion] Selecting columns of a matrix

[Keith Goodman]

Alan G Isaac wrote:

> M.transpose()[V>0]
> If you want the columns as columns,
> you can transpose again.

I can't get that to work when M is a n by m matrix:

>> M = asmatrix(rand(3,4))

>> M

matrix([[ 0.78970407,  0.78681448,  0.79167808,  0.57857822],
       [ 0.44567836,  0.23985597,  0.49392248,  0.0282004 ],
       [ 0.7044725 ,  0.4090776 ,  0.12035218,  0.71365101]])

>> V = asmatrix(rand(4,1))

>> V

matrix([[ 0.61638738],
       [ 0.76928157],
       [ 0.3882811 ],
       [ 0.68979661]])

>> M.transpose()[V > 0.5]
matrix([[ 0.78970407,  0.78681448,  0.57857822]])

The answer should be a 3 by 3 matrix.