# 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))

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
>
>
> __________________________________________________
>
>
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help