# How to perform cross-year date operations on rasters?

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## How to perform cross-year date operations on rasters?

 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  Thanks in advance,  -- Thiago V. dos Santos PhD student Land and Atmospheric Science University of Minnesota _______________________________________________ R-sig-Geo mailing list [hidden email] https://stat.ethz.ch/mailman/listinfo/r-sig-geo
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## Re: How to perform cross-year date operations on rasters?

 On Thu, 5 Nov 2015 at 09:38 Thiago V. dos Santos <[hidden email]> 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 > [hidden email] > https://stat.ethz.ch/mailman/listinfo/r-sig-geo>         [[alternative HTML version deleted]] _______________________________________________ R-sig-Geo mailing list [hidden email] https://stat.ethz.ch/mailman/listinfo/r-sig-geo
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## Re: 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 <[hidden email]> wrote: On Thu, 5 Nov 2015 at 09:38 Thiago V. dos Santos <[hidden email]> 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 >[hidden email] >https://stat.ethz.ch/mailman/listinfo/r-sig-geo> _______________________________________________ R-sig-Geo mailing list [hidden email] https://stat.ethz.ch/mailman/listinfo/r-sig-geo