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

[Glynn Clements]

G. Allegri 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.
> This would let us do filtering (with row/columns offsets) as it is done in
> r.neighbors, where the NULL values are directly discarded.

In 7.0, I've added nmin, nmax, nmedian and nmode functions which
ignore nulls.

-- 
Glynn Clements <glynn at gclements.plus.com>