[R] sum with dates

[Enrico Schumann]

If "adding x years to a date" means "increase the YYYY part of a date by 
x", then it should be easiest to manipulate the character representation 
of your date.

dates <- as.Date(c("2001-01-12","2001-02-12","2001-03-12"))

addYear <- function(d,addyears) {
     Y <- as.numeric(strftime(d, "%Y")) + addyears
     as.Date(paste(Y, strftime(d,"-%m-%d"), sep = ""))
}

## (There are leapyears with more than 365 days.)
dates + 365*15
addYear(dates,15)

That said, you cannot "go one year ahead" from February 29, unless you 
go ahead by 4, 8, 12, ... years (unless the new year is divisible by 100 
but not by 400). One possibility would be to leave such dates as Feb 28.

addYear <- function(d,addyears) {
     Y <- as.numeric(strftime(d, "%Y")) + addyears
     YisLeapyear <- Y%%400==0L | ((Y%%4==0L) & !(Y%%100==0L))
     mdpart <- strftime(d,"-%m-%d")
     mdpart <- ifelse(mdpart == "-02-29" & YisLeapyear,
                      mdpart, "-02-28")
     as.Date(paste(Y, mdpart, sep = ""))

}

dates <- as.Date(c("2001-01-12","2001-02-12","2001-03-12",
                    "1899-02-28","1896-02-29","2000-03-01"))
addYear(dates,4)
addYear(dates,5)
addYear(dates,8)



Regards,
Enrico



Am 13.12.2011 04:17, schrieb R. Michael Weylandt:
> It depends how your dates are stored, but generally you can just add
> 365*15 to them. E.g.,
>
> print(x<- Sys.Date())
> print(x + 365*15)
>
> So for you,
>
> dataset$dates<- dataset$dates + 365*15
>
> Michael
>
> On Mon, Dec 12, 2011 at 9:39 PM, Ana<rrasterr at gmail.com>  wrote:
>> How do I sum 15 years to my dataset?
>>
>> original dataset
>>          dates        val
>> 1    2001-01-12    1.2
>> 2    2001-02-12    1.2
>> 3    2001-03-12    1.2
>>
>> result
>>          dates        val
>> 1 2016-01-12 1.2
>> 2    2016-02-12 1.2
>> 3    2016-03-12 1.2
>>
>> ______________________________________________
>> 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.
>
> ______________________________________________
> 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.
>

-- 
Enrico Schumann
Lucerne, Switzerland
http://nmof.net/