What do you mean by 'standard time'? If you mean UTC, set TZ=UTC. For anything else, see ?Sys.timezone (which explains the use of TZ).

I am guessing that you are storing times in "POSIXct" objects (you do not say): they are in UTC. Have you any evidence that 'datetimes are getting converted to daylight savings times'? More likely they are getting *printed* in your local timezone, because that is the documented default behaviour. But you can change it (see ?format.POSIXct).

You are attributing self-will to R in 'an ORACLE database that R is importing data in from': it is merely following instructions. We don't have those instructions and there is no sign of a package that could do this in your sessionInfo (R itself has no such facilities). If the Oracle database is not in your local timezone (which seems to be the case) you will need to tell the import facilty what time it is in. If the (non-R) import facility does this right, the datetimes will be marked as being in UTC (or whatever), and most of the time printed as such (but I would always do so explicitly).

The difference betwee 2.6.2 and later versions is that lots of bugs in the way Windows handles timezones were fixed, so it sounds as if you have been relying on a Windows bug.

On Fri, 27 Feb 2009, Rhiannon Marchant wrote:


  Hi all,
  I've been having some trouble with times in regards to daylight savings in R
  version 2.8.1.  I have an ORACLE database that R is importing data in from,
  for the 2am and 2:30am time intervals for the dates that daylight savings
  starts the times are getting read as NA values into R. I'm also finding that
  if  I  open a R workspace from version 6.2.2,the datetimes are getting
  converted to daylight savings times.  The times are a cruical part of my
  analysis and need to stay in standard time. I would like to be using a newer
  version of R than I am currently using (2.6.2) so that I can make use of the
  newer packages that are available, however with this problem of the time
  conversions I am unable to do this. Is anyone able to help with to set up
  R2.8.1 to use standard time instead of daylight savings times?

[...]

--
Brian D. Ripley,                  rip...@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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