Don asks a good question. Here is the analogy from the grid package.
> library(grid)
> unit(12, "in")
[1] 12in
> unit(12, "cm")
[1] 12cm
> unit.c(unit(12, "in"), unit(12, "cm"))
[1] 12in 12cm
> c(unit(12, "in"), unit(12, "cm"))
[1] 12 12
> ?unit
> convertUnit(c(unit(12, "in"), unit(12, "cm")), "in")
Error in convertUnit(c(unit(12, "in"), unit(12, "cm")), "in") :
'x' argument must be a unit object
> convertUnit(unit.c(unit(12, "in"), unit(12, "cm")), "in")
[1] 12in 4.7244094488189in
>
On Fri, Apr 7, 2017 at 6:33 PM, MacQueen, Don <macque...@llnl.gov> wrote:
> I think a more illuminating inspection is this:
>
>> attributes(A)
> $class
> [1] "POSIXct" "POSIXt"
>
> $tzone
> [1] "UTC"
>
>> attributes(B)
> $class
> [1] "POSIXct" "POSIXt"
>
> $tzone
> [1] "UTC"
>
>> attributes(C)
> $class
> [1] "POSIXct" "POSIXt"
>
> Note that the operation c(A,B) loses the $tzone attribute.
>
> Note also that C[1] and A[1] are actually the same point in time -- my
> default time zone, PDT, is 7 hours behind UTC -- but they display
> differently, due to the different tzone attribute.
>> C[1]
> [1] "2013-03-27 23:00:00 PDT"
>> A[1]
> [1] "2013-03-28 06:00:00 UTC"
>
>> A[1]==C[1]
> [1] TRUE
>
> Finally, if I do this:
> attributes(C)$tzone <- attributes(A)$tzone
>
> Then they display the same:
>> C[1]
> [1] "2013-03-28 06:00:00 UTC"
>> A[1]
> [1] "2013-03-28 06:00:00 UTC"
>
> It's a tossup whether resetting the lost attribute is preferable to setting
> the system timezone.
>
> Then there's the design question of whether the c() operation should lose the
> tzone attribute. In this case it would be nice if it didn't, but what should
> happen if we use c() on two objects with different tzone attributed??
>
> --
> Don MacQueen
>
> Lawrence Livermore National Laboratory
> 7000 East Ave., L-627
> Livermore, CA 94550
> 925-423-1062
>
>
> On 4/7/17, 12:48 AM, "R-help on behalf of Troels Ring"
> <r-help-boun...@r-project.org on behalf of tr...@gvdnet.dk> wrote:
>
> Thanks a lot - good idea:
>
> I put
>
> Sys.setenv(TZ = "UTC")
>
> ahead of the code - solves the problem!
>
> Thanks a lot
>
>
> Den 07-04-2017 kl. 09:26 skrev Mark Leeds:
> > Hi Troels: This is off-list so as to not clog the list with my noise
> > because my suggestion may not work. I really don't know that much
> > about time-zones. but. I ran your code and it "worked" but all the
> > times were correctly time stamped but they changed from UTC to GMT.
> > in time-zone. In your
> > case, they changed to something and the time got shifted it looks
> > like. So, definitely it has to do with how your time-zones are set. In
> > my .Rprofile, I have something.
> > Let me check. ... time passes ..... I have below in my .Rprofile. So
> > my guess is that, if you want things to remain UTC, then put below
> > in your .Rprofile but change it from "GMT" to "UTC". Others may have
> > different solutions but that might work. If you don't have that, then
> > R decides what to use and I'm not sure how it decides.
> >
> > Sys.setenv(TZ = "GMT")
> >
> > #print("LOADING MASS LIBRARY")
> > #ibrary("MASS")
> > #print("LOADING LATTICE LIBRARY")
> > #library("lattice")
> >
> >
> >
> >
> > :~>
> >
> > On Fri, Apr 7, 2017 at 3:00 AM, Troels Ring <tr...@gvdnet.dk
> > <mailto:tr...@gvdnet.dk>> wrote:
> >
> > Thanks a lot - perhaps it is just understanding how times dates
> > are handled, sorry to bother if that is just the case
> >
> > C[1]==A[1] # TRUE
> >
> > but
> >
> > C[1]
> > [1] "2013-03-28 07:00:00 CET"
> > A[1]
> > [1] "2013-03-28 06:00:00 UTC"
> >
> >
> >
> >
> >
> >
> > Den 07-04-2017 kl. 08:27 skrev Ulrik Stervbo:
> >
> > Hi Troels,
> >
> > I get no error. I think we need more information to be of any
> > help.
> >
> > Best wishes,
> > Ulrik
> >
> > On Fri, 7 Apr 2017 at 08:17 Troels Ring <tr...@gvdnet.dk
> > <mailto:tr...@gvdnet.dk>> wrote:
> >
> > Dear friends - I have further problems handling
> > dates_times, as
> > demonstrated below where concatenating two formatted
> > vectors of
> > date_times results in errors.
> > I wonder why this happens and what was wrong in trying to
> > take these two
> > vectors together
> > All best wishes
> > Troels Ring
> > Aalborg, Denmark
> > Windows
> > R version 3.3.2 (2016-10-31)
> >
> >
> > A <- structure(c(1364450400, 1364450400, 1364536800,
> > 1364623200,
> > 1364709600,
> > 1364796000, 1364882400, 1364968800, 1365055200,
> > 1365141600, 1365228000,
> > 1365314400, 1365400800), class = c("POSIXct", "POSIXt"),
> > tzone = "UTC")
> > A
> > B <- structure(c(1365141600, 1365228000, 1365314400,
> > 1365400800,
> > 1365487200,
> > 1365573600, 1365660000, 1365746400, 1365832800,
> > 1365919200, 1366005600,
> > 1366092000), class = c("POSIXct", "POSIXt"), tzone = "UTC")
> > B
> > C <- c(A,B)
> > C
> >
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