[R] unwanted switch to DST with POSIXct objects

[Denis Chabot]

Thanks Jeff and Spencer, I will probably set the time zone for my session, but I had forgotten the possibility of setting the time zone attribute of a POSIXct object, which would have solved my problem also.

Denis
Le 2011-06-05 à 11:14, Spencer Graves a écrit :

> On 6/5/2011 9:30 AM, Jeff Newmiller wrote:
>> Sys.setenv(TZ="Etc/GMT+5")
> 
> Or:
> 
> x <- as.POSIXct(as.Date('2011-01-15'))
> attr(x, 'tzone') <- "Etc/GMT+5"
> x
> 
> 
>      This version works without Sys.setenv, which may not work on some platforms.  Unfortunately, I believe there are some copy operations that lose attributes like tzone, so you need to check.
> 
> 
>      For some of the most advanced and complicated time series problems, you might consider what's available from the Rmetrics project, e.g., at "https://www.rmetrics.org/ebooks":  They are designed to deal with coordinating trading data from financial markets all over the world, each of which affects all the others but have different trading hours.
> 
> 
>      Hope this helps.
>      Spencer
> 
>> Make the timezone you prefer the default for that R session.
>> 
>> FWIW: EST may or may not exist as a valid timezone on your system, but it is an ambiguous notation anyway.
>> ---------------------------------------------------------------------------
>> Jeff Newmiller The ..... ..... Go Live...
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>> ---------------------------------------------------------------------------
>> Sent from my phone. Please excuse my brevity.
>> 
>> Denis Chabot<chabot.denis at gmail.com>  wrote:
>> 
>> Hi,
>> 
>> For a project I try to keep everything in normal time, not daylight saving time, to prevent problem when instruments collected data during the nights when we go from DST to normal time.
>> 
>> But sometimes R tricks me and I do not know how to prevent it.
>> 
>> This is one example:
>> 
>> lights_on = as.POSIXct(c("2011-05-06 04:09:26", "2011-05-07 04:07:53", "2011-05-08 04:06:21",
>> "2011-05-09 04:04:51", "2011-05-10 04:03:22", "2011-05-11 04:01:55",
>> "2011-05-12 04:00:30", "2011-05-13 03:59:06", "2011-05-14 03:57:45",
>> "2011-05-15 03:56:25", "2011-05-16 03:55:07"), tz="EST") # not DST
>> 
>> lights_off = as.POSIXct(c("2011-05-05 18:56:54", "2011-05-06 18:58:19", "2011-05-07 18:59:44",
>> "2011-05-08 19:01:08", "2011-05-09 19:02:32", "2011-05-10 19:03:55",
>> "2011-05-11 19:05:18", "2011-05-12 19:06:40", "2011-05-13 19:08:01",
>> "2011-05-14 19:09:22", "2011-05-15 19:10:42" ), tz="EST")	# not DST
>> 
>> (a = lights_on[c(1,5)])	# not DST
>> [1] "2011-05-06 04:09:26 EST" "2011-05-10 04:03:22 EST"
>> 
>> (b = lights_off[c(2,6)])	# not DST
>> [1] "2011-05-06 18:58:19 EST" "2011-05-10 19:03:55 EST"
>> 
>> (x = c(lights_off[2], lights_on[2])) # suddenly DST
>> [1] "2011-05-06 19:58:19 EDT" "2011-05-07 05:07:53 EDT"
>> 
>> Why did x end up in DST? How could I prevent it?
>> 
>> Thanks in advance,
>> 
>> Denis
>> _____________________________________________
>> 
>> 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.
>> 
>> 
>> 	[[alternative HTML version deleted]]
>> 
>> ______________________________________________
>> 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.
>> 
> 
> 
> -- 
> Spencer Graves, PE, PhD
> President and Chief Operating Officer
> Structure Inspection and Monitoring, Inc.
> 751 Emerson Ct.
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