Many thanks for the responses about how to read datetimes into POSIXct
which refer to straight GMT times without regard to Daylight Saving. To
reiterate, I''m using R 2.0.0 on win2000.
I have tried Gabor's suggestion,see below, which did not work for me. The
fundamental setting (for me) appears to be in the registry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation
The values here are most readily altered using the 'Date/ TIme properties'
window (just double click the wee digital clock on the right of the window
task bar). When I disable Daylight Saving a registry variable
called DisableAutoDaylightTimeSet is created and is set to 1. This can be
observed with regedit. Now all works perfectly with my date handling. So
it seems that setting the timezone to GMT is necessary but not sufficient
for my needs
I confess that I do not understand the relationship between setting
registry variables and environment (eg TZ="GMT").
In practice I would like to keep my win200 machine with Daylight Saving
enabled - for the sake of other applications. One strategy is to make the
required registry alterations immediately before and after any R code which
handles dates. But then I'm rather worried whether continuously enabling /
disabling Daylight Saving would have dire consequences for other
applications and the well-being of my already shaky OS. Is this the right
route - and if so could someone please guide me how to achieve this in R
for win2000?
Perhaps a better strategy would be to introduce some set-able option within
R that forced date handling to ignore Daylight Saving. But here I have
insufficient expertise and can only appeal to the continuing generosity of
the developer community.
I am sure that there are many R users in the same position as me - but
perhaps they don't all realize it!