I am sorry, I meant to post this in a different thread... On Wed, Dec 3, 2014 at 8:32 PM, Benjamin Root <ben.r...@ou.edu> wrote:
> 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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