On Sep 13, 2010, at 1:24 PM, Andrew Yee wrote:
> Thanks David, now I wonder how you can have as.Date() render the
> date using local time rather than UTC.
>
Since we are both in the EDT TZ at the moment, our times are UTC-4
(hours = 60*60 seconds)
> dt <- as.POSIXct("2010-08-22 23:14:52")
> as.Date(dt -60*60*4)
Now == [1] "2010-08-22"
> #was [1] "2010-08-23"
There are probably more elegant and self-documenting methods, but I'm
not fully versed in TZ conumdrums.
--
David.
> Andrew
>
> On Mon, Sep 13, 2010 at 12:08 PM, David Winsemius <dwinsem...@comcast.net
> > wrote:
>
> On Sep 13, 2010, at 11:56 AM, Andrew Yee wrote:
>
> I'm trying to understand why as.Date() is converting a the modified
> date of
> a file from August 22 to August 23.
>
> foo <- file.info(file.to.process)
> str(foo)
> 'data.frame': 1 obs. of 10 variables:
> $ size : num 5.37e+09
> $ isdir : logi FALSE
> $ mode :Class 'octmode' int 436
> $ mtime : POSIXct, format: "2010-08-22 23:14:52"
> $ ctime : POSIXct, format: "2010-09-13 11:34:31"
> $ atime : POSIXct, format: "2010-09-09 15:42:00"
> $ uid : int 503
> $ gid : int 503
> $ uname : chr "ayee"
> $ grname: chr "ayee"
>
> as.Date(foo$mtime)
> [1] "2010-08-23"
>
> In this case as.Date(foo$mtime) gives August 23. I would have
> expected
> August 22.
>
> You are pretty close to midnight. Probably a TZ issue. Check your
> locale settings versus UTC/GMT.
>
> > dt <- as.POSIXct("2010-08-22 23:14:52")
> > as.Date(dt)
> [1] "2010-08-23"
>
> Happens to me too, but when its 23:14 here, (US-EDT) it's the next
> day in Greenwich. The help page says:
> "The last [POSIXct] is converted to days by ignoring the time after
> midnight in the representation of the time in UTC." That is not
> entirely clear to my reading, but I am forced to conclude that it
> means as.Date returns the Date in UTC terms rather than in local
> terms.
>
> --
> David.
>
>
> Thanks,
> Andrew
>
> sessionInfo()
> R version 2.11.1 Patched (2010-09-11 r52901)
> Platform: x86_64-unknown-linux-gnu (64-bit)
>
> locale:
> [1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C
> [3] LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8
> [5] LC_MONETARY=C LC_MESSAGES=en_US.UTF-8
> [7] LC_PAPER=en_US.UTF-8 LC_NAME=C
> [9] LC_ADDRESS=C LC_TELEPHONE=C
> [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
>
> attached base packages:
> [1] stats graphics grDevices utils datasets methods base
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@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.
>
> David Winsemius, MD
> West Hartford, CT
>
>
David Winsemius, MD
West Hartford, CT
[[alternative HTML version deleted]]
______________________________________________
R-help@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.
