Having a large stack of timeserie rasters I would like to create another rasterstack which represents 5-day rolling sum per each pixel across the layers. Given the size of the raster stack, the raster::calc runs endlessly for this task, and I was therefore wondering if this operation could be implemented faster using the terra::lapp. However:
library(terra)
stack_A<-rast(nlyrs=10)
rollsum<-function(x){data.table::frollsum(x,n=5)}
stack_B<-lapp(stack_A, fun=rollsum)
returns an error:
"Error in (function (x) :
unused arguments (c(0, 0,...
or: [lapp] I do not like 'fun' :("
Id be gratefull if somebody could suggest where the mistake is, or maybe suggest another implementation (stars::?)
You can use terra::app for that; terra::app is equivalent to raster::calc. You tried terra::lapp, that method is equivalent to raster::overlay.
library(terra)
library(data.table)
f <- system.file("ex/logo.tif", package="terra")
r <- rast(c(f,f,f,f))
rollsum <- function(x){data.table::frollsum(x,n=5)}
x <- app(r, rollsum)
I am not sure if this will be much faster, as the bottleneck probably is the rollsum function.
"terra" has a function roll for this and I expect that to be much faster.
library(terra)
#terra 1.6.47
f <- system.file("ex/logo.tif", package="terra")
r <- rast(c(f,f,f,f))
y <- roll(r, 5, "sum", type="to")