[GRASS-dev] Determine raster rank order per raster cell

[Paulo van Breugel]

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 at data, 1, function(x){
     rank(x, na.last="keep", ties.method="average")
})
lyrs at 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?

Cheers

Paulo
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