A slightly different way to look at it (I don't think it is exactly the same problem, but the description reminded me of it):
http://mail.scipy.org/pipermail/numpy-discussion/2013-April/066269.html (and I think there are some things that can be done to make that faster, but I don't recall it right now) Ben Root On Tue, Apr 16, 2013 at 4:35 PM, Bradley M. Froehle <brad.froe...@gmail.com> wrote: > Hi Bryan: > > On Tue, Apr 16, 2013 at 1:21 PM, Bryan Woods <bwo...@aer.com> wrote: > >> I'm trying to do something that at first glance I think should be simple >> but I can't quite figure out how to do it. The problem is as follows: >> >> I have a 3D grid Values[Nx, Ny, Nz] >> >> I want to slice Values at a 2D surface in the Z dimension specified by >> Z_index[Nx, Ny] and return a 2D slice[Nx, Ny]. >> >> It is not as simple as Values[:,:,Z_index]. >> >> I tried this: >> >>> values.shape >> (4, 5, 6) >> >>> coords.shape >> (4, 5) >> >>> slice = values[:,:,coords] >> >>> slice.shape >> (4, 5, 4, 5) >> >>> slice = np.take(values, coords, axis=2) >> >>> slice.shape >> (4, 5, 4, 5) >> >>> >> >> Obviously I could create an empty 2D slice and then fill it by using >> np.ndenumerate to fill it point by point by selecting values[i, j, >> Z_index[i, j]]. This just seems too inefficient and not very pythonic. >> > > The following should work: > > >>> values.shape > (4,5,6) > >>> coords.shape > (4,5) > >>> values[np.arange(values.shape[0])[:,None], > ... np.arange(values.shape[1])[None,:], > ... coords].shape > (4, 5) > > Essentially we extract the values we want by values[I,J,K] where the > indices I, J and K are each of shape (4,5) [or broadcast-able to that > shape]. > > > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@scipy.org > http://mail.scipy.org/mailman/listinfo/numpy-discussion > >
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