[GRASS-dev] adding a flag to discard NULL values in mapalgebra aggregation functions

[Margherita Di Leo]

Hi Giovanni, all,

On Wed, Jun 20, 2012 at 12:17 PM, G. Allegri <giohappy at gmail.com> wrote:

> Following a thread I've opened on the grass-users list, I would like to
> suggest a proposal to add a flag, to the r.mapcalc command, to discrd
> NULL values when evaluating aggregation functions like max(), min(),
> mode(), etc.
> Looking into the code of, for example., the max() function [1], it seems
> that if a NULL value is in the set of the arguments, the result is set to
> NULL (if I understand it correctly).
> With the proposed flag, I would like to ask r.mapcalc to do not consider
> the NULLs, and to the calculations only on the not-NULL subset of values.
>

Shouldn't it be the default behavior?

ciao madi



> This would let us do filtering (with row/columns offsets) as it is done in
> r.neighbors, where the NULL values are directly discarded.
>
> giovanni
>
> [1]
> http://trac.osgeo.org/grass/browser/grass/trunk/raster/r.mapcalc/xmax.c
>
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-- 
Dr. Margherita Di Leo
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