[R-sig-Geo] Incorrect month order in zApply function

[Kay Kilpatrick]

Hi

The various Apply functions always return the output in simple 
alphabetical order when the factor label is a character, regardless of 
the order of the factor in the calling argument.

Ben had a correct solution --- simply reorder the output from Zapply.

Alternatively you could use a numeric representation for the month label 
using by = as.numeric(months(x). The output would then be in increasing 
numeric order from 1 -12.

I do not believe Vijay's suggestion is proper. It does not reorder the 
output --- instead it changes the label of a given monthly mean eg. The 
value for Jan. would then be labeled as Apr.

k

On 7/28/16 10:52 PM, Thiago V. dos Santos via R-sig-Geo wrote:
> Dear all,
>
> I am using the raster package to calculate monthly averages of climatic variables.
>
> Essentially, this is the function I use:
>
> library(raster)
>
> # Create date sequence
> idx <- seq(as.Date("1996/1/1"), as.Date("2010/12/31"), by = "day")
>
> # Create raster stack and assign dates
> r <- raster(ncol=5, nrow=5)
> s <- stack(lapply(1:length(idx), function(x) setValues(r, runif(ncell(r)))))
> s <- setZ(s, idx)
>
> # Calculate monthly average
> x <- zApply(s, by=months, mean, name=month.abb[])
>
> names(x)
> [1] "April" "August" "December" "February" "January" "July" "June"
> [8] "March" "May" "November" "October" "September"
> getZ(x)
> [1] "April" "August" "December" "February" "January" "July" "June"
> [8] "March" "May" "November" "October" "September"
>
>
> The problem here is the output of both names(x) and getZ(x). It looks like a random month order is returned (even though I provide the labels), which makes me confused about the results.
>
>
> By performing the same calculation in a different software and comparing the results, I came to realize that the order of months for the results by raster should, in fact, be Jan-Feb-Mar-Apr-May-Jun-Jul-Aug-Sep-Oct-Nov-Dec
>   
> How can I control the way raster delivers the object names after using zApply, in order to sort the months in the "natural" order?
>
> Greetings, -- Thiago V. dos Santos
>
> PhD student
> Land and Atmospheric Science
> University of Minnesota
>
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-- 
Katherine (Kay) Kilpatrick
University of Miami/RSMAS
Ocean Science Department
Satellite Remote Sensing Laboratory
MSC 231
4600 Rickenbacker Cswy
Miami, Fl
ph: 305-962-3069
kkilpatrick at rsmas.miami.edu