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

[Dominik Schneider]

Could you use water years for your dates? so Oct-Sep is the same year and
then subset based on month and water year.


On Thu, Nov 5, 2015 at 11:17 AM, Thiago V. dos Santos <
thi_veloso at yahoo.com.br> wrote:

> 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
> >
> >_______________________________________________
> >R-sig-Geo mailing list
> >R-sig-Geo at r-project.org
> >https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> >
>
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at r-project.org
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>

	[[alternative HTML version deleted]]