[R-sig-Geo] Monthly loop in raster stack with daily data

[Thiago V. dos Santos]

Hi all,

I am working with very large raster stacks. Each stack is a time-series climate forecast, where the layers are *daily* values of a given meteorological variable (say temperature).

How can I loop through the *months* in the raster and count the number of *days* above a certain threshold?


Please see the code below showing a raster with two years of daily data:

#Create a rasterStack similar to my data - same dimensions and layer names
r <- raster(ncol=360, nrow=180)
s <- stack(lapply(1:730, function(x) setValues(r, runif(ncell(r),min=0,max=30))))
idx <- seq(as.Date("2010/1/1"), by = "day", length.out = 730)
s <- setZ(s, idx)
s

hot.days <- calc(s, function(x,na.rm) sum(x) > 25) # I need to do this for every month in the raster stack, counting the number of days where temperature is greater than 25.

The final raster would have 24 layers (12 months x 2 years) with the count of days.

Is this analysis possible to be done on a raster or should I convert the data to a different format?
Thanks a lot,
 -- Thiago V. dos Santos

PhD student
Land and Atmospheric Science
University of Minnesota