[R] unwanted switch to DST with POSIXct objects

[Spencer Graves]

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.
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>
> 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
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>
> ______________________________________________
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> 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.
San José, CA 95126
ph:  408-655-4567