format(d, "%U") and format(d, "%W") give week numbers using
different conventions. See ?strptime
On Thu, Dec 11, 2008 at 7:43 AM, Gustaf Rydevik
<[EMAIL PROTECTED]> wrote:
> Hi all,
>
> Is there a simple function already implemented for getting the ISO
> weeks of a Date object?
> I couldn't find one, and so wrote my own function to do it, but would
> appreciate a pointer to the "default" way. If a function is not yet
> implemented, could the code below be of interest to submit to CRAN?
>
> Best Regards,
>
> Gustaf
>
> --------------------
>
> getweek<-function(Y,M=NULL,D=NULL){
>
> if(!class(Y)[1]%in%c("Date","POSIXt")) {
> date.posix<-strptime(paste(c(Y,M,D),collapse="-"),"%Y-%m-%d")
> }
> if(class(Y)[1]%in%c("POSIXt","Date")){
> date.posix<-as.POSIXlt(Y)
> Y<-as.numeric(format(date.posix,"%Y"))
> M<-as.numeric(format(date.posix,"%m"))
> D<-as.numeric(format(date.posix,"%d"))
> }
>
>
> LY<- (Y%%4==0 & !(Y%%100==0))|(Y%%400==0)
> LY.prev<- ((Y-1)%%4==0 & !((Y-1)%%100==0))|((Y-1)%%400==0)
> date.yday<-date.posix$yday+1
> jan1.wday<-strptime(paste(Y,"01-01",sep="-"),"%Y-%m-%d")$wday
> jan1.wday<-ifelse(jan1.wday==0,7,jan1.wday)
> date.wday<-date.posix$wday
> date.wday<-ifelse(date.wday==0,7,date.wday)
>
>
> ####If the date is in the beginning, or end of the year,
> ### does it fall into a week of the previous or next year?
> Yn<-ifelse(date.yday<=(8-jan1.wday)&jan1.wday>4,Y-1,Y)
> Yn<-ifelse(Yn==Y&((365+LY-date.yday)<(4-date.wday)),Y+1,Y)
>
> ##Set the week differently if the date is in the beginning,middle or
> end of the year
>
> Wn<-ifelse(
> Yn==Y-1,
> ifelse((jan1.wday==5|(jan1.wday==6 &LY.prev)),53,52),
> ifelse(Yn==Y+1,1,(date.yday+(7-date.wday)+(jan1.wday-1))/7-(jan1.wday>4))
> )
> return(list(Year=Yn,ISOWeek=Wn))
> }
>
>
> --
> Gustaf Rydevik, M.Sci.
> tel: +46(0)703 051 451
> address:Essingetorget 40,112 66 Stockholm, SE
> skype:gustaf_rydevik
>
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
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