How to perform cross-year date operations on rasters?

Thanks for your input Michael. With slight modifications on your
suggestion, I almost got there:

library(raster)
library(zoo)

# 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)))))
idx <- seq(as.Date("2010/1/1"), by = "day", length.out = 1825)
s <- setZ(s, idx)

# Separate layers with months of interest
ldates <- format(getZ(s), "%m") %in% c("10", "11", "12", "01")
s2 <- subset(s, which(ldates))

# Apply function
s3 <- zApply(s2, by=as.yearmon, fun = sum)


The problem now is that the "isolated" january in the first year is also
taken into account, and the "isolated" oct-nov-dec in the last year as well.

Ideally the function would run only on the contiguous period:
oct-nov-dec-jan, and not when at least one month is missing (for example in
the first and last years of the series).

Still possible to achieve this?
Greetings,
 -- Thiago V. dos Santos

PhD student
Land and Atmospheric Science
University of Minnesota



On Thursday, November 5, 2015 12:15 AM, Michael Sumner <mdsumner at gmail.com>
wrote:







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