Re: [R] POSIXct time zone and daylight savings issues
On Mon, 30 Oct 2006, Sebastian P. Luque wrote: Hi again, A related issue I can't quite understand is: R tt - as.POSIXct(2006-05-24, tz=EEST) R tt [1] 2006-05-24 EEST R seq(tt, length=12, by=months) [1] 2006-05-24 EEST 2006-06-24 EEST 2006-07-24 EEST 2006-08-24 EEST [5] 2006-09-24 EEST 2006-10-24 EEST 2006-11-24 EEST 2006-12-24 EEST [9] 2007-01-24 EEST 2007-02-24 EEST 2007-03-24 EEST 2007-04-24 EEST R tt - as.POSIXct(2006-05-24, tz=EET) R seq(tt, length=12, by=months) [1] 2006-05-24 EEST 2006-06-24 EEST 2006-07-24 EEST 2006-08-24 EEST [5] 2006-09-24 EEST 2006-10-24 EEST 2006-11-24 EET 2006-12-24 EET [9] 2007-01-24 EET 2007-02-24 EET 2007-03-24 EET 2007-04-24 EEST R sessionInfo() R version 2.4.0 (2006-10-03) x86_64-pc-linux-gnu locale: LC_CTYPE=en_CA.UTF-8;LC_NUMERIC=C;LC_TIME=en_CA.UTF-8;LC_COLLATE=en_CA.UTF-8;LC_MONETARY=en_CA.UTF-8;LC_MESSAGES=en_CA.UTF-8;LC_PAPER=en_CA.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_CA.UTF-8;LC_IDENTIFICATION=C attached base packages: [1] methods stats graphics grDevices utils datasets [7] base other attached packages: lattice 0.14-9 i.e. daylight savings 'tzone' attribute gets adjusted automatically when providing the standard time attribute, but not when providing the daylight savings time. Does this behaviour depend on the OS/locale? Should the 'tz' argument supplied when creating POSIXct objects always be the standard time version? No, it should be a timezone, and the timezone specification includes when DST is in effect. See ?as.POSIXct for details and references of timezones. For example, EST is a timezone without DST and EST5EDT is a timezone with DST (and they agree in winter). It looks like Linux is interpreting EEST as UTC+3 throughout the year (which appears not to be used anywhere as an actual timezone). So the behaviour is clear: EEST does not have DST, and $isdst == 0 in that 'timezone', whereas EET does have DST. -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UKFax: +44 1865 272595 __ 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 and provide commented, minimal, self-contained, reproducible code.
Re: [R] POSIXct time zone and daylight savings issues
On Tue, 31 Oct 2006 09:24:02 + (GMT), Prof Brian Ripley [EMAIL PROTECTED] wrote: [...] No, it should be a timezone, and the timezone specification includes when DST is in effect. See ?as.POSIXct for details and references of timezones. For example, EST is a timezone without DST and EST5EDT is a timezone with DST (and they agree in winter). It looks like Linux is interpreting EEST as UTC+3 throughout the year (which appears not to be used anywhere as an actual timezone). So the behaviour is clear: EEST does not have DST, and $isdst == 0 in that 'timezone', whereas EET does have DST. Thanks for this explanation. Very important to check whether the supplied 'tz' is really interpreted as a valid time zone by the OS! Cheers, -- Seb __ 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 and provide commented, minimal, self-contained, reproducible code.
Re: [R] POSIXct time zone and daylight savings issues
Hi again, A related issue I can't quite understand is: R tt - as.POSIXct(2006-05-24, tz=EEST) R tt [1] 2006-05-24 EEST R seq(tt, length=12, by=months) [1] 2006-05-24 EEST 2006-06-24 EEST 2006-07-24 EEST 2006-08-24 EEST [5] 2006-09-24 EEST 2006-10-24 EEST 2006-11-24 EEST 2006-12-24 EEST [9] 2007-01-24 EEST 2007-02-24 EEST 2007-03-24 EEST 2007-04-24 EEST R tt - as.POSIXct(2006-05-24, tz=EET) R seq(tt, length=12, by=months) [1] 2006-05-24 EEST 2006-06-24 EEST 2006-07-24 EEST 2006-08-24 EEST [5] 2006-09-24 EEST 2006-10-24 EEST 2006-11-24 EET 2006-12-24 EET [9] 2007-01-24 EET 2007-02-24 EET 2007-03-24 EET 2007-04-24 EEST R sessionInfo() R version 2.4.0 (2006-10-03) x86_64-pc-linux-gnu locale: LC_CTYPE=en_CA.UTF-8;LC_NUMERIC=C;LC_TIME=en_CA.UTF-8;LC_COLLATE=en_CA.UTF-8;LC_MONETARY=en_CA.UTF-8;LC_MESSAGES=en_CA.UTF-8;LC_PAPER=en_CA.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_CA.UTF-8;LC_IDENTIFICATION=C attached base packages: [1] methods stats graphics grDevices utils datasets [7] base other attached packages: lattice 0.14-9 i.e. daylight savings 'tzone' attribute gets adjusted automatically when providing the standard time attribute, but not when providing the daylight savings time. Does this behaviour depend on the OS/locale? Should the 'tz' argument supplied when creating POSIXct objects always be the standard time version? Cheers, -- Seb __ 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 and provide commented, minimal, self-contained, reproducible code.
Re: [R] POSIXct time zone and daylight savings issues
I don't know the answer to your question but if you are using dates with no times and don't need time zones (both of which appear to be the case here) then you could use Date class and avoid the issue altogether. See the help desk article in R News 4/1 where there is a discussion of how to choose the date time class. On 10/30/06, Sebastian P. Luque [EMAIL PROTECTED] wrote: Hi again, A related issue I can't quite understand is: R tt - as.POSIXct(2006-05-24, tz=EEST) R tt [1] 2006-05-24 EEST R seq(tt, length=12, by=months) [1] 2006-05-24 EEST 2006-06-24 EEST 2006-07-24 EEST 2006-08-24 EEST [5] 2006-09-24 EEST 2006-10-24 EEST 2006-11-24 EEST 2006-12-24 EEST [9] 2007-01-24 EEST 2007-02-24 EEST 2007-03-24 EEST 2007-04-24 EEST R tt - as.POSIXct(2006-05-24, tz=EET) R seq(tt, length=12, by=months) [1] 2006-05-24 EEST 2006-06-24 EEST 2006-07-24 EEST 2006-08-24 EEST [5] 2006-09-24 EEST 2006-10-24 EEST 2006-11-24 EET 2006-12-24 EET [9] 2007-01-24 EET 2007-02-24 EET 2007-03-24 EET 2007-04-24 EEST R sessionInfo() R version 2.4.0 (2006-10-03) x86_64-pc-linux-gnu locale: LC_CTYPE=en_CA.UTF-8;LC_NUMERIC=C;LC_TIME=en_CA.UTF-8;LC_COLLATE=en_CA.UTF-8;LC_MONETARY=en_CA.UTF-8;LC_MESSAGES=en_CA.UTF-8;LC_PAPER=en_CA.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_CA.UTF-8;LC_IDENTIFICATION=C attached base packages: [1] methods stats graphics grDevices utils datasets [7] base other attached packages: lattice 0.14-9 i.e. daylight savings 'tzone' attribute gets adjusted automatically when providing the standard time attribute, but not when providing the daylight savings time. Does this behaviour depend on the OS/locale? Should the 'tz' argument supplied when creating POSIXct objects always be the standard time version? Cheers, -- Seb __ 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 and provide commented, minimal, self-contained, reproducible code. __ 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 and provide commented, minimal, self-contained, reproducible code.
[R] POSIXct time zone and daylight savings issues
Hello,
Suppose we need a function that takes a POSIXct object and need to
calculate the time difference between it and GMT time:
gmtDiff - function(time) {
time.gmt - as.POSIXct(format(time, tz=GMT))
time.plt - as.POSIXlt(time)
dlstime - ifelse(time.plt$isdst 0, 1, 0)
timezone - as.numeric(difftime(time, time.gmt, units=hours))
timezone - dlstime
}
Please note this assumes no daylight savings if the 'isdst' component for
the POSIXlt object is negative (i.e. don't know if DST is in effect). Now
if we pass some values to this function:
R gmtDiff(as.POSIXct(2006-10-27, tz=GMT))
[1] -5
R gmtDiff(as.POSIXct(Sys.time()))
[1] -6
I would have expected the first call to return zero, but it seems as if
the calculation is always done with respect to the system's locale, and I
can't understand what the function of the 'tzone' attribute is in these
calculations. ?strptime has information on how to change the locale for
some operations, which in this case didn't change the outcome:
R lct - Sys.getlocale(LC_TIME); Sys.setlocale(LC_TIME, C)
[1] C
R gmtDiff(as.POSIXct(2006-10-27, tz=GMT))
[1] -5
R gmtDiff(as.POSIXct(Sys.time()))
[1] -6
R Sys.setlocale(LC_TIME, lct)
[1] en_CA.UTF-8
R sessionInfo()
R version 2.4.0 (2006-10-03)
x86_64-pc-linux-gnu
locale:
LC_CTYPE=en_CA.UTF-8;LC_NUMERIC=C;LC_TIME=en_CA.UTF-8;LC_COLLATE=en_CA.UTF-8;LC_MONETARY=en_CA.UTF-8;LC_MESSAGES=en_CA.UTF-8;LC_PAPER=en_CA.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_CA.UTF-8;LC_IDENTIFICATION=C
attached base packages:
[1] methods stats graphics grDevices utils datasets
[7] base
other attached packages:
lattice
0.14-9
I'd be grateful for any clarification and advice on how to properly
calculate this time difference.
Cheers,
--
Seb
__
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
and provide commented, minimal, self-contained, reproducible code.
Re: [R] POSIXct time zone and daylight savings issues
Try this:
gmtDiff - function(time) time - as.POSIXct(format(time), tz = GMT)
gmtDiff(Sys.time())
gmtDiff(as.POSIXct(2006-10-27, tz = GMT))
which both give me the correct answer currently.
The expression after the minus sign comes from the table at the end
of the help desk article in R News 4/1. I think you got the parentheses
wrong in your version and I think the isdst calculation needs to
be omitted -- I get the right answer if I leave it out but wrong with it.
On 10/27/06, Sebastian P. Luque [EMAIL PROTECTED] wrote:
Hello,
Suppose we need a function that takes a POSIXct object and need to
calculate the time difference between it and GMT time:
gmtDiff - function(time) {
time.gmt - as.POSIXct(format(time, tz=GMT))
time.plt - as.POSIXlt(time)
dlstime - ifelse(time.plt$isdst 0, 1, 0)
timezone - as.numeric(difftime(time, time.gmt, units=hours))
timezone - dlstime
}
Please note this assumes no daylight savings if the 'isdst' component for
the POSIXlt object is negative (i.e. don't know if DST is in effect). Now
if we pass some values to this function:
R gmtDiff(as.POSIXct(2006-10-27, tz=GMT))
[1] -5
R gmtDiff(as.POSIXct(Sys.time()))
[1] -6
I would have expected the first call to return zero, but it seems as if
the calculation is always done with respect to the system's locale, and I
can't understand what the function of the 'tzone' attribute is in these
calculations. ?strptime has information on how to change the locale for
some operations, which in this case didn't change the outcome:
R lct - Sys.getlocale(LC_TIME); Sys.setlocale(LC_TIME, C)
[1] C
R gmtDiff(as.POSIXct(2006-10-27, tz=GMT))
[1] -5
R gmtDiff(as.POSIXct(Sys.time()))
[1] -6
R Sys.setlocale(LC_TIME, lct)
[1] en_CA.UTF-8
R sessionInfo()
R version 2.4.0 (2006-10-03)
x86_64-pc-linux-gnu
locale:
LC_CTYPE=en_CA.UTF-8;LC_NUMERIC=C;LC_TIME=en_CA.UTF-8;LC_COLLATE=en_CA.UTF-8;LC_MONETARY=en_CA.UTF-8;LC_MESSAGES=en_CA.UTF-8;LC_PAPER=en_CA.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_CA.UTF-8;LC_IDENTIFICATION=C
attached base packages:
[1] methods stats graphics grDevices utils datasets
[7] base
other attached packages:
lattice
0.14-9
I'd be grateful for any clarification and advice on how to properly
calculate this time difference.
Cheers,
--
Seb
__
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
and provide commented, minimal, self-contained, reproducible code.
__
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
and provide commented, minimal, self-contained, reproducible code.
Re: [R] POSIXct time zone and daylight savings issues
On Fri, 27 Oct 2006 14:55:15 -0400, Gabor Grothendieck [EMAIL PROTECTED] wrote: Try this: gmtDiff - function(time) time - as.POSIXct(format(time), tz = GMT) gmtDiff(Sys.time()) gmtDiff(as.POSIXct(2006-10-27, tz = GMT)) which both give me the correct answer currently. The expression after the minus sign comes from the table at the end of the help desk article in R News 4/1. I think you got the parentheses wrong in your version and I think the isdst calculation needs to be omitted -- I get the right answer if I leave it out but wrong with it. Thanks Gabor, this provides the correct result, and the isdst calculation is no longer needed. Cheers, -- Seb __ 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 and provide commented, minimal, self-contained, reproducible code.
