[Numpy-discussion] Grid indexing

Ian Stokes-Rees ijstokes at hkl.hms.harvard.edu
Mon Feb 28 09:21:55 EST 2011

On 2/26/11 3:36 AM, Wolfgang Kerzendorf wrote:
> I have a n dimensional grid. The grids axes are linear but not 
> intergers. Let's say I want the value in gridcell [3.2,-5.6,0.01]. Is 
> there an easy way to transform the index? Do I have to write my own 
> class to accomplish this. Is there an easy way in numpy to accomplish 
> this. Can I give functions to transform the index somehow to the numpy 
> array?

I can't answer this definitively, but this sounds like a tough one to
find builtin -- the idea of array indexing is very tightly tied to
integers starting from zero.  I think you'll need to map from your grid
coordinate system to an integer system (and vice-versa).  If you can
come up with a linear transformation for each dimension that map your
floats to non-negative ints, that is probably pretty fast and easy for
single cell lookups.  Sparse arrays could be helpful if the data isn't
"dense" on your grid.


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