[R] Aggregating on Water Year Rather Than Calendar Year

[Clint Bowman]

Aha!  I was unclear of the way to extract the year from the function call 
(which your example shows.)  The following works wonders:

w$w.year<-as.POSIXlt(w$d+7948800)$year+1900

Again, thanks,

Clint

On Wed, 16 Jun 2004, Don MacQueen wrote:

> It's not clear where your problem is.
> 
> Did w$w.year come out wrong?
> Or did the aggregate() function fail?
> 
> For getting the water year, I would do it differently:
>   (this is for a U.S. English locale, and minimally tested)
> 
>     tmp <- as.POSIXlt(w$d)$year+1900
>     w$w.year <- ifelse( format(w$d,'%b') %in% c('Oct','Nov','Dec'), tmp+1, tmp)
> 
> Then you can do things like
>    table(w$w.year)
>    table(w$w.year,w$param.name)
> to help find out if w.year came out like it should.
> 
> You'll have to provide error messages or something if the problem is 
> with using aggregate().
> 
> At 11:21 AM -0700 6/16/04, Clint Bowman wrote:
> >The US water year extends from 01 October yyyy-1 through 30 September yyyy
> >and is referenced by the year starting on the included 01 January yyyy. 
> >I'd like to be able to find the annual means for the water year.  To do so
> >I've taken the input date-time, which is in the usual format
> >
> >"1991-10-07 10:35:00"
> >
> >changed it by:
> >
> >w$d<-as.POSIXct(w$date.time)
> >
> >Now I can add an offset of 92 days
> >
> >w$w.year<-as.POSIXct(w$d+7948800)
> 
> Try   w$w.year <- w$d+7948800
> 
> >
> >and have the years correspond to the "water year."
> >
> >Now I wish to obtain some means by something like:
> >
> >waterT<-aggregate(w$value[w$param.name=="Temperature"],
> >list(w$w.year[w$param.name=="Temperature"]),mean)
> >
> >Except that I need to work on the year and being a neophyte in date
> >arithmetic I'm not finding a working method.
> >
> >TIA
> >
> >Clint
> >
> >--
> >Clint Bowman			INTERNET:	clint at ecy.wa.gov
> >Air Quality Modeler		INTERNET:	clint at math.utah.edu
> >Department of Ecology		VOICE:		(360) 407-6815
> >PO Box 47600			FAX:		(360) 407-7534
> >Olympia, WA 98504-7600
> >
> 
> -Don
> 
> 

-- 
Clint Bowman			INTERNET:	clint at ecy.wa.gov
Air Quality Modeler		INTERNET:	clint at math.utah.edu
Department of Ecology		VOICE:		(360) 407-6815
PO Box 47600			FAX:		(360) 407-7534
Olympia, WA 98504-7600