[R-sig-Geo] How to calculate decadal average and percent change in raster stacks?

[Thiago V. dos Santos]

Dear all,

I am working with yearly climate projections of rainfall that cover the period from 2010 to 2099:

library(raster)

# Create the date sequence
idx <- seq(as.Date("2010/1/1"), as.Date("2099/12/31"), by = "year")

# Create raster stack and apply the date
r <- raster(ncol=360, nrow=180)
s <- stack(lapply(1:length(idx), function(x) setValues(r, runif(ncell(r)))))
s <- setZ(s, idx)
s

Given this raster stack, how can I calculate the average values per decade and percent change for each decade?

I define decades here as 2010-2019, 2020-2029, 2030-2039 and so on until 2090-2099.

I guess the real issue here is how to "split" a raster stack in decades. Any ideas?  
Thanks,
 -- Thiago V. dos Santos

PhD student
Land and Atmospheric Science
University of Minnesota