How to perform cross-year date operations on rasters?
On Thu, 5 Nov 2015 at 09:38 Thiago V. dos Santos <thi_veloso at yahoo.com.br> wrote:
Dear all,
Consider that I have a raster stack with daily values. How can I perform
date operations covering a time interval that crosses years?
For example, I want to sum the values from every october-to-january period
in this sample raster:
library(raster)
# Create a rasterStack similar to cmip5 - same dimensions and layer names
r <- raster(ncol=180, nrow=90)
s <- stack(lapply(1:1825, function(x) setValues(r, runif(ncell(r)))))
# Apply time stamps to raster
#x <- as.Date(c("2010-01-01","2014-12-31"),format="%Y-%m-%d")
#difftime(x[2], x[1], units="days")
idx <- seq(as.Date("2010/1/1"), by = "day", length.out = 1825)
s <- setZ(s, idx)
s
You can subset on the dates, by running a test on the date values:
ldates <- format(getZ(s), "%m") %in% c("10", "11", "01")
subsetting the object
subset(s, which(ldates))
and finally calculating what you want
calc(subset(s, which(ldates)), sum)
HTH
Thanks in advance, -- Thiago V. dos Santos PhD student Land and Atmospheric Science University of Minnesota
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