R help - Jun 2012 - Define a variable on a non-standard year interval (Water Years)

Hello,

I am trying to define a different interval for a "year". In hydrology,
a "water year" is defined as the period between October 1st and
September 30 of the following year. I was wondering how I might do
this in R. Say I have a data.frame like the following and I want to
extract a variable with the water year specs as defined above:

df<-data.frame(Date=seq(as.Date("2000/10/1"),
as.Date("2003/9/30"), "days"))

## Extract the normal year
df$year <- factor(format(as.Date(df$Date), "%Y"))

So the question is how might I define a variable that extends from
October 1st to September 30th rather than the normal January 1st to
December 31st?

Thanks in advance!

Sam

Here's one way.
(not including the conversion to factor)

wdf <- data.frame(Date=seq(as.Date("2000/10/1"),
as.Date("2003/9/30"),
"days"))


wdf$wyr <- as.numeric(format(wdf$Date,'%Y'))
is.nxt <-  as.numeric(format(wdf$Date,'%m')) %in% 1:9
wdf$wyr[ is.nxt ] <- wdf$wyr[is.nxt]-1

## and you can do some rudimentary checking with:
table(format(wdf$Date,'%Y'), wdf$wyr)

Note that df is the name of an R-supplied function and therefore not a
good choice for one's own use.


(By the way, thank you for providing easy to recreate example data.
As a minor point, this:
wdf <- data.frame(Date=seq(as.Date("2000/10/1"),
                           as.Date("2003/9/30"),
                           "3 weeks"))
would be just a little easier to work with for testing)



-- 
Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062





On 6/11/12 10:22 AM, "Sam Albers" <tonightsthenight at
gmail.com> wrote:
>Hello,
>
>I am trying to define a different interval for a "year". In
hydrology,
>a "water year" is defined as the period between October 1st and
>September 30 of the following year. I was wondering how I might do
>this in R. Say I have a data.frame like the following and I want to
>extract a variable with the water year specs as defined above:
>
>df<-data.frame(Date=seq(as.Date("2000/10/1"),
as.Date("2003/9/30"),
>"days"))
>
>## Extract the normal year
>df$year <- factor(format(as.Date(df$Date), "%Y"))
>
>So the question is how might I define a variable that extends from
>October 1st to September 30th rather than the normal January 1st to
>December 31st?
>
>Thanks in advance!
>
>Sam
>
>______________________________________________
>R-help at r-project.org mailing list
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.

On Mon, Jun 11, 2012 at 1:22 PM, Sam Albers <tonightsthenight at
gmail.com> wrote:
> Hello,
>
> I am trying to define a different interval for a "year". In
hydrology,
> a "water year" is defined as the period between October 1st and
> September 30 of the following year. I was wondering how I might do
> this in R. Say I have a data.frame like the following and I want to
> extract a variable with the water year specs as defined above:
>
> df<-data.frame(Date=seq(as.Date("2000/10/1"),
as.Date("2003/9/30"), "days"))
>
> ## Extract the normal year
> df$year <- factor(format(as.Date(df$Date), "%Y"))
>
> So the question is how might I define a variable that extends from
> October 1st to September 30th rather than the normal January 1st to
> December 31st?
>
See this:

https://stat.ethz.ch/pipermail/r-help/2004-June/052952.html


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