[Numpy-discussion] transform an array of points efficiently?
Keith Goodman
kwgoodman@gmail....
Thu Jul 9 21:22:40 CDT 2009
On Thu, Jul 9, 2009 at 7:08 PM, Chris Colbert<sccolbert@gmail.com> wrote:
> say i have an Nx4 array of points and I want to dot every [n, :] 1x4
> slice with a 4x4 matrix.
>
> Currently I am using apply_along_axis in the following manner:
>
> def func(slice, mat):
> return np.dot(mat, slice)
>
> np.apply_along_axis(func, arr, 1, mat)
>
> Is there a more efficient way of doing this that doesn't require a
> python function for each slice?
I'm sure I'm missing an important point, but can't you solve the whole
problem with one dot:
>> x = np.random.rand(3,4)
>> y = np.random.rand(4,4)
>> np.dot(x, y)
array([[ 0.86488057, 0.23456114, 0.91592677, 0.89798689],
[ 1.24197754, 0.39907686, 1.45453141, 1.13645076],
[ 1.41419289, 0.81818818, 1.09768428, 1.32719635]])
>> np.dot(x[0,:], y)
array([ 0.86488057, 0.23456114, 0.91592677, 0.89798689])
>> np.dot(x[1,:], y)
array([ 1.24197754, 0.39907686, 1.45453141, 1.13645076])
>> np.dot(x[2,:], y)
array([ 1.41419289, 0.81818818, 1.09768428, 1.32719635])
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