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

[Dutrieux, Loic]

Hi Thiago,

Building on Michael's answer and your example, I think the following should work. The tricky part is to build the right by= argument for zApply().
You can see zApply as a wrapper of aggregate.zoo() for temporal raster bricks, and you're more likely to find answers for aggregate.zoo than for zApply when searching the internet.
This is where I found the answer: https://stat.ethz.ch/pipermail/r-help/2008-August/171366.html

Cheers,
Loïc Dutrieux

library(raster)
library(zoo)
library(lubridate)

# 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=year(as.yearmon(getZ(s2)) - 1/12), fun = sum))

On 11/05/2015 07:17 PM, Thiago V. dos Santos 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
>>
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>>
>
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