summing rasters with a condition given by other rasters

Hi,

Hi Ben,

many thanks for the detailed answer. The code works fine, but when I use
rasters for eos and sos instead of numbers, i get an error:



b <- brick(system.file("external/rlogo.grd", package="raster"))

b <- addLayer(b,b,b)
b

sos <- raster(system.file("external/rlogo.grd", package="raster"))
eos <- raster(system.file("external/rlogo.grd", package="raster"))


sum_segment <- function(x, from = sos, to = eos, ...) {
 sum(x[from:to],...)
}

s <- calc(b, sum_segment)

Error in .calcTest(x[1:5], fun, na.rm, forcefun, forceapply) : 
 cannot use this function

am I doing something wrong?

Yes, as tempting as it is to do otherwise you really do have to use numeric position indices.  Inside the function sum_segment the value of x is simple a numeric vector. Within the scope of the function the context of the pixels embedded in the raster object is temporarily "lost" - they are just a vector of numbers.  

To work with the calc() function you must first compute the position indices for sos and eos using which().

sos <- which(names(b) == "blue.1")  # you would substitue the name of your layer for blue.1
eos <- which(names(b) == "green.3") # and again for green.3

Cheers,
Ben

--
View this message in context: http://r-sig-geo.2731867.n2.nabble.com/summing-rasters-with-a-condition-given-by-other-rasters-tp7588222p7588226.html
Sent from the R-sig-geo mailing list archive at Nabble.com.

_______________________________________________
R-sig-Geo mailing list
R-sig-Geo at r-project.org
https://stat.ethz.ch/mailman/listinfo/r-sig-geo

Ben Tupper
Bigelow Laboratory for Ocean Sciences
60 Bigelow Drive, P.O. Box 380
East Boothbay, Maine 04544
http://www.bigelow.org