Re: [R] given a mid-month date, get the month-end date

From: Whit Armstrong <whit_at_twinfieldscapital.com>
Date: Tue 20 Dec 2005 - 04:50:41 EST


Or add a month, then subtract a day:

Ndays <- function(posix.ct.dates,days) {

    # one day = 60*60*24 = 86400 seconds     ans <- as.POSIXct(posix.ct.dates) + 86400*days

    # we only have a problem if the date went from     # DST to ST or from ST to DST
    ans + (as.POSIXlt(posix.ct.dates)$isdst - as.POSIXlt(ans)$isdst)*3600
}

calendar.eom <- function(x) {

    x.lt <- as.POSIXlt(x)
    mon <- x.lt $mon + 2
    year <- x.lt$year

    # if month was December add a year
    year <- year + as.integer(mon==13)
    mon[mon==13] <- 1

    Ndays(ISOdate(1900+year,mon,1,hour=0,tz=attr(x,"tzone")),-1) }

x <- seq(as.POSIXct("2001-01-10"),as.POSIXct("2005-12-10"),by="months") data.frame(before=x,after=calendar.eom(x))

-----Original Message-----
From: r-help-bounces@stat.math.ethz.ch
[mailto:r-help-bounces@stat.math.ethz.ch] On Behalf Of Gabor Grothendieck
Sent: Monday, December 19, 2005 11:59 AM To: t c
Cc: r-help
Subject: Re: [R] given a mid-month date, get the month-end date

The zoo package has a yearmon class with as methods which can be used:

library(zoo)
dd <- Sys.Date() # test data

as.Date(as.yearmon(dd), frac = 1)

as.yearmon converts the "Date" class date to a year and month of class "yearmon" dropping the day and representing it internally in a way consistent with "ts" class.

as.Date above then converts it back to "Date" class. Since yearmon dates have no day (they are just a year and a month) the frac argument is used to indicate what fraction of the month to use as the day of the month so frac = 0 (the
default) would give the beginning of the month) and frac = 1 gives the end.

On 12/19/05, t c <quantpm@yahoo.com> wrote:
> I have a vector of dates.
>
> I wish to find the month end date for each.
>
> Any suggestions?
>
> e.g.
>
> For 12/15/05, I want 12/31/05,
>
> For 10/15/1995, I want 10/31/1995, etc
>
>
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R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Dec 20 04:55:18 2005

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