[R] Difference between times

Prof Brian Ripley ripley at stats.ox.ac.uk
Sun Apr 20 09:50:36 CEST 2014

On 18/04/2014 21:46, David Winsemius wrote:
> On Apr 18, 2014, at 12:59 PM, Prof Brian Ripley wrote:
>> On 18/04/2014 19:46, Rui Barradas wrote:
>>> Hello,
>>> The reason why is that you've misspelled CET (not CEST)
>> Neither CET nor CEST are portable time-zone names.  We have not been given the 'at a minimum' information required by the posting guide, so please read ?Sys.timezone on your system.
> Dear Prof;
> Thanks for the impetus to yet again read that page. Despite frequently reading help pages and in particular reading that one many times, I still was not getting the 'tz' arguments correct on a Mac. I do now see that I was spelling my TZ incorrectly (as "Americas/Los_Angeles" rather than "America/Los_Angeles".
> Fellow Mac users may face a problem when using the Finder unless they set it up to display hidden ('dot') files. The /usr/ folder is "greyed out" but it still does open. If I restore my Finder defaults to not show system files and folders, I no longer see that directory and would not have been able to resolve my spelling error on my own:
>> dt2 = as.POSIXct("2014-04-18 09.00", format="%Y-%m-%d %H.%M", tz = "America/New_York")
>>   dt1 = as.POSIXct("2014-04-18 09.00", format="%Y-%m-%d %H.%M", tz = "America/Los_Angeles")
>>   dt1-dt2
> Time difference of 3 hours
> I don't suppose a warning could be issued by the as.POSIXct code when a "tz" argument is not found in the database to let people know that 'UTC' will be the default?

No, as the underlying POSIX function does not report this.  We could 
perhaps do this on platforms which use --with-internal-tzcode but not 
e.g. on Linux.

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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