[R] Extent of time zone vulerability for POSIX date and time classes

[Gabor Grothendieck]

There are several ways:

1. the default number of year digits is set by the chron.year.abb option.
The R News article mentions this in the Avoiding Errors section but
does suggest you not set it.

options(chron.year.abb = FALSE)
chron(1)

2. Alternately, define:

out.fmt <- function(x) with( month.day.year(x),
	sprintf("%02.f/%02.f/%04.f", month, day, year))

# Now any of these will work:
x <- chron(1:5)
out.fmt(x)

# or

x <- chron(1:5)
chron(x, out.format = out.fmt)

# or

x <- chron(1:5, out.format = out.fmt)
x


On 4/5/07, Tim Bergsma <timb at metrumrg.com> wrote:
> Gabor,
>
> thanks for the feedback. I like the idea of coercing the system time
> zone, and sticking with strptime/strftime.  The balance would probably
> tip in favor of chron, however, if I could get the format correct.
> Apparently the default is two-digit year:
>
> library(chron)
> chron(1)
> [1] 01/02/70
>
> chron(1,format="m/d/y")
> [1] 01/02/70
>
> But I need four digit year, so I try:
>
> chron(1,format="m/d/yyyy")
> [1] Jan/02/1970
>
> Now, month has switched to character!  I don't know of a format
> convention that gets it back to numeric (although conventions are
> documented for forcing to character).  Comment?
>
> Regards,
>
> Tim.
>
>
> Gabor Grothendieck wrote:
> > If you use
> >
> > Sys.putenv(TZ = "GMT")
> >
> > at the beginning of your session then local time zone and GMT time
> > zone will be the same so you should not have a problem.  This was
> > not possible, at least on Windows, at the time the R News article
> > was written.
> >
> >
> >
> >
> >
> > On 4/5/07, Tim Bergsma <timb at metrumrg.com> wrote:
> >> Hi.
> >>
> >> I frequently convert date and time data to and from character
> >> representations.  I'm frustrated with chron, because 'seconds' are
> >> required to create a time object (my input data never has seconds).
> >
> > You could use paste:
> >
> >  times(paste("12:30", 0, sep = ":"))
> >
> > and make it into a function if you use it a lot.
> >
> >> More importantly, I cannot make chron print the format 12/30/2006 (which
> >> my output data requires).
> >
> > That is the default output format so you don't have to specify anything.
> > Its
> > only with POSIX that its not the default.  For example:
> >
> >> library(chron)
> >> x <- chron("12/30/2006")
> >> x
> > [1] 12/30/06
> >
> >>
> >> I really like the format flexibility of strftime() and strptime(), but
> >> of course am paranoid about timezone issues.  After reading the standard
> >> reference several times
> >> (http://cran.r-project.org/doc/Rnews/Rnews_2004-1.pdf), I am tempted to
> >> conclude that if I never specify timezones, and never use Sys.time(),
> >> the vulnerabilities do not pertain.
> >
> > That won't protect you but this would let you use POSIX safely:
> >
> > http://www.mail-archive.com/r-help@stat.math.ethz.ch/msg83508.html
> >
> >>
> >> To the point: if I'm merely converting to and from character data that
> >> does not represent time zones, is there still a time zone vulnerability
> >> with strftime() and strptime()?
> >>
> >> Thanks in advance,
> >>
> >> Tim Bergsma, PhD
> >> Metrum Research Group, LLC
> >>
> >>
> >> #example
> >> strftime(
> >>   strptime(
> >>     "30-Dec-06 23:30",
> >>     format="%d-%b-%y %H:%M"
> >>   ),
> >>   format="%m/%d/%Y %H:%M"
> >> )
> >> [1] "12/30/2006 23:30"
> >>
> >> ______________________________________________
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> >> 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.
> >>
> >
> >
>