On Thu 23 Jan 2014 11:15:17 AM CET, Moritz Lennert wrote:
On 22/01/14 23:20, Paulo van Breugel 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 how efficient this would be, but how about using
r.mapcalc with something like this for each map:
Y1 = if(X1>X2, if(X1>X3, 1, 2), if(X1>X3, 2, 3))
Moritz
Thanks Moritz,
I had thought about that, works good for few maps, but it gets a bit
unwieldy with e.g., 40 maps. I'll try though if I can split the if
function somehow.
Cheers,
Paulo
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