Hi Paulo
On 22 January 2014 23:20, Paulo van Breugel <p.vanbreu...@gmail.com> wrote:
> Does anybody know a smart way to calculate for X rasters per raster cell the
> rank order of those rasters? For example, if I have three rasters X1, X2 and
> X3:
>
> X1 X2 X3
> 1 3 2
> 2 5 8
> 5 1 3
> NA 8 2
>
> would give three new raster layers with the values:
>
> Y1 Y2 Y3
> 1 3 2
> 1 2 3
> 3 1 2
> NA 2 1
>
> I am now reading the rasters in R and using a combination of apply() and
> rank() function to create new raster layers:
>
> in <- c("X1", "X2", "X3")
> lyrs <- readRAST6(in)
> tmp <- apply(lyrs@data, 1, function(x){
> rank(x, na.last="keep", ties.method="average")
> })
> lyrs@data <- t(tmp)
>
> I am sure there are better ways in R, but especially when dealing with very
> large raster layers, I was hoping there is a way to do this directly in
> GRASS GIS. Or otherwise, would it be difficult to create a function for
> this?
>
I don't know if the result is what you are looking for but with python
I do something like this
from grass.pygrass.raster import RasterNumpy
import scipy.stats as sstats
map = RasterNumpy('YOURMAP')
map.open()
newmap = RasterNumpy('YOURNEWMAP', 'w')
newmap.open()
i = 0
for row in map:
newmap[i] = sstats.rankdata(row)
i+=1
newmap.close()
map.close()
I tested it, but when I close the map it return the error "Bus error"
> Cheers
>
> Paulo
>
--
ciao
Luca
http://gis.cri.fmach.it/delucchi/
www.lucadelu.org
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