From jorismeys at gmail.com  Thu May 18 13:45:16 2017
From: jorismeys at gmail.com (Joris Meys)
Date: Thu, 18 May 2017 13:45:16 +0200
Subject: [Rd] [R] R-3.4.0 fails test
In-Reply-To: <29540304-FC8B-4B49-B94B-E191DEFA3BCB@gmail.com>
References: <20170517074216.GA4553@slingshot.co.nz>
 <4a086fbb-61ed-d3a5-ce23-14bbaea5531f@gmail.com>
 <ACA47D66-F469-4C75-8521-CB0DD76572C7@gmail.com>
 <20170518090016.GB4553@slingshot.co.nz>
 <29540304-FC8B-4B49-B94B-E191DEFA3BCB@gmail.com>
Message-ID: <CAO1zAVarefFWaW_UmN6gCN3ppVuaGhLO7ErYdpUJmbfJ6rb4XQ@mail.gmail.com>

This has to do with your own timezone. If I run that code on my computer,
both formats are correct. If I do this after

Sys.setenv(TZ = "UTC")

Then:

> cbind(format(dlt), format(dct))
      [,1]                  [,2]
 [1,] "2016-12-06 21:45:41" "2016-12-06 20:45:41"
 [2,] "2016-12-06 21:45:42" "2016-12-06 20:45:42"

The reason for that, is that dlt has a timezone set, but dct doesn't. To be
correct, it only takes the first value "", which indicates "Use the default
timezone of the locale".

> attr(dlt, "tzone")
[1] ""     "CET"  "CEST"
> attr(dct, "tzone")
[1] ""

The thing is, in POSIXlt the timezone attribute is stored together with the
actual values for hour, minute etc. in list format. Changing the timezone
doesn't change those values, but it will change the time itself:

> Sys.unsetenv("TZ")
> dlt2 <- dlt
> attr(dlt2,"tzone") <- "UTC"
> dlt2
 [1] "2016-12-06 21:45:41 UTC" "2016-12-06 21:45:42 UTC"
 [3] "2016-12-06 21:45:43 UTC" "2016-12-06 21:45:44 UTC"

in POSIXct the value doesn't change either, just the attribute. But this
value is the number of seconds since the origin. So the time itself doesn't
change, but you'll see a different hour.

> dct
 [1] "2016-12-06 21:45:41 CET" "2016-12-06 21:45:42 CET"
...
> attr(dct,"tzone") <- "UTC"
> dct
 [1] "2016-12-06 20:45:41 UTC" "2016-12-06 20:45:42 UTC"
 [3] "2016-12-06 20:45:43 UTC" "2016-12-06 20:45:44 UTC"

So what you see, is simply the result of your timezone settings on your
computer.

Cheers
Joris

On Thu, May 18, 2017 at 1:19 PM, peter dalgaard <pdalgd at gmail.com> wrote:

>
> > On 18 May 2017, at 11:00 , Patrick Connolly <p_connolly at slingshot.co.nz>
> wrote:
> >
> > On Wed, 17-May-2017 at 01:21PM +0200, Peter Dalgaard wrote:
> >
> > |>
> > |> Anyways, you might want to
> > |>
> > |> a) move the discussion to R-devel
> > |> b) include your platform (hardware, OS) and time zone info
> >
> > System:    Host: MTA-V1-427894 Kernel: 3.19.0-32-generic x86_64 (64 bit
> gcc: 4.8.2)
> >           Desktop: KDE Plasma 4.14.2 (Qt 4.8.6) Distro: Linux Mint 17.3
> Rosa
>
> I suppose that'll do...
>
>
> > Time zone: NZST
>
>
>
> >
> > |> c) run the offending code lines "by hand" and show us the values of
> format(dlt) and format(dct) so we can see what the problem is, something
> like
> > |>
> > |> dlt <- structure(
> > |>     list(sec = 52, min = 59L, hour = 18L, mday = 6L, mon = 11L, year
> = 116L,
> > |>        wday = 2L, yday = 340L, isdst = 0L, zone = "CET", gmtoff =
> 3600L),
> > |>        class = c("POSIXlt", "POSIXt"), tzone = c("", "CET", "CEST"))
> > |> dlt$sec <- 10000 + 1:10
> > |> dct <- as.POSIXct(dlt)
> > |> cbind(format(dlt), format(dct))
> >
> >> cbind(format(dlt), format(dct))
> >      [,1]                  [,2]
> > [1,] "2016-12-06 21:45:41" "2016-12-06 22:45:41"
> > [2,] "2016-12-06 21:45:42" "2016-12-06 22:45:42"
> > [3,] "2016-12-06 21:45:43" "2016-12-06 22:45:43"
> > [4,] "2016-12-06 21:45:44" "2016-12-06 22:45:44"
> > [5,] "2016-12-06 21:45:45" "2016-12-06 22:45:45"
> > [6,] "2016-12-06 21:45:46" "2016-12-06 22:45:46"
> > [7,] "2016-12-06 21:45:47" "2016-12-06 22:45:47"
> > [8,] "2016-12-06 21:45:48" "2016-12-06 22:45:48"
> > [9,] "2016-12-06 21:45:49" "2016-12-06 22:45:49"
> > [10,] "2016-12-06 21:45:50" "2016-12-06 22:45:50"
> >>
> >
>
>
> So exactly 1 hour out of whack. Is there a Daylight Saving Times issue,
> perchance?
>
> -pd
>
>
> >
> > --
> > ~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.
> >   ___    Patrick Connolly
> > {~._.~}                   Great minds discuss ideas
> > _( Y )_                Average minds discuss events
> > (:_~*~_:)                  Small minds discuss people
> > (_)-(_)                             ..... Eleanor Roosevelt
> >
> > ~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.
>
> --
> Peter Dalgaard, Professor,
> Center for Statistics, Copenhagen Business School
> Solbjerg Plads 3, 2000 Frederiksberg, Denmark
> Phone: (+45)38153501
> Office: A 4.23
> Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>



-- 
Joris Meys
Statistical consultant

Ghent University
Faculty of Bioscience Engineering
Department of Mathematical Modelling, Statistics and Bio-Informatics

tel :  +32 (0)9 264 61 79
Joris.Meys at Ugent.be
-------------------------------
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[Rd] [R] R-3.4.0 fails test
Joris Meys