[R-sig-Geo] How to perform cross-year date operations on rasters?

[Thiago V. dos Santos]

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
>
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