Treatment of Date ODBC objects in R (RODBC)

Ivan Alves wrote:

Dear all,

Retrieving an Oracle "Date" data type by means of RODBC (version 1.2-4) I 
get different classes in R depending on which operating system I am in:

On MacOSX I get "Date" class
On Windows I get " "POSIXt" "POSIXct" class

The problem is material, as converting the "POSIXt" "POSIXct" object with 
as.Date() returns one day less ("2008-12-17 00:00:00 CET" is returned as 
"2008-12-16").

This is in a sense correct since CET is one hour ahead of GMT (two hours in 
Summer). What is a bit puzzling is that

ISOdate(2008,12,24)

[1] "2008-12-24 12:00:00 GMT"

class(ISOdate(2008,12,24))

[1] "POSIXt"  "POSIXct"

as.POSIXct("2008-12-24")

[1] "2008-12-24 CET"

as.POSIXct("2008-12-24")+1

[1] "2008-12-24 00:00:01 CET"

I.e. we have two ways of converting a timeless date to POSIXct, and they 
differ in noon/midnight, and in whether local timezone matters or not.

I believe Brian did this, and he usually does things for a reason....

I have 2 related questions:

1. Is there a way to control the conversion used by RODBC for types "Date"? 
or is this controlled by the ODBC Driver (in my case the Oracle driver in 
Windows and Actual on Mac OS X)?

2. What is the trick to get as.Date() to return the _intended_ date (the 
date that the OS X environment "correctly" reads)?

Add 12 hours, maybe? (43200 seconds)

Or play around with the timezone, but that seems painful.

--
  O__  ---- Peter Dalgaard             ?ster Farimagsgade 5, Entr.B
 c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)              FAX: (+45) 35327907