Thx - that did the trick. But why the 'Oh dear'?
// [[Rcpp::export]]
Rcpp::NumericVector getDT(int dt) {
Rcpp::NumericVector res(1);
res[0] = dt;
res.attr("tzone") = "GMT";
res.attr("class") = CharacterVector::create("POSIXct", "POSIXt");;
return res;
}
On Mon, Jan 12, 2015 at 1:34 PM, Dirk Eddelbuettel <edd at debian.org> wrote:
On 12 January 2015 at 13:10, janus Larsen wrote:
| Hi again,
|
| Thanks Dirk for your reply. So there is no way of doing this on the C
side?
|
| The thing is that I'm returning a large object that contains a lot of
| information (about an unstructured 3D model) and some of the fields are
| DateTimes. I could of cource wrap the call to the C function in an R
function
| that then corrects the dates to GMT (or sets the timezone before calling
the C
| function), but it just not that nice... Previously I had this code
written
| using <RDefines.h> where I could set the timezone on the returned posIXct
| object:
|
| SEXP long2DateTime(long dt) {
| SEXP result;
| result = PROTECT(allocVector(REALSXP, 1));
| REAL(result)[0] = dt;
| SEXP gmt = PROTECT(allocVector(STRSXP,1));
| SET_STRING_ELT(gmt, 0, mkChar("GMT"));
| SEXP tzone = PROTECT(allocVector(STRSXP,1));
| SET_STRING_ELT(tzone, 0, mkChar("tzone"));
| setAttrib(result, tzone, gmt);
| SEXP datetimeclass = PROTECT(allocVector(STRSXP,2));
| SET_STRING_ELT(datetimeclass, 0, mkChar("POSIXt"));
| SET_STRING_ELT(datetimeclass, 1, mkChar("POSIXct"));
| setAttrib(result, R_ClassSymbol, datetimeclass);
| UNPROTECT(4);
| return result;
| }
Oh dear. See eg http://gallery.rcpp.org/articles/creating-xts-from-c++/ or
the other few xts related answers on the Rcpp Gallery.
Dirk
| Janus
|
| On Fri, Jan 9, 2015 at 1:22 PM, Dirk Eddelbuettel <edd at debian.org>
wrote:
|
|
| On 9 January 2015 at 11:50, janus Larsen wrote:
| | Hi,
| | How do I set the timezone on an Rcpp::Datetime?
| | Thanks in advance,
| | Sunaj
| |
| | This returns "1970-01-01 01:00:00 CET" (computer setting), but I
want
| GMT...
|
| R does the formatting in its session based on your locale.
|
| That is generally the right thing:
|
| | // [[Rcpp::export]]
| | Rcpp::Datetime test() {
| | double d=0;
| | return(d);
| | }
|
| Small corrections to your code to actually export the function
(under a
| safer
| name):
|
| #include <Rcpp.h>
|
| // [[Rcpp::export]]
| Rcpp::Datetime timetest(double d=0) {
| return(d);
| }
|
| Then:
|
| R> sourceCpp("/tmp/timeQ.cpp")
| R> timetest() # my default is Chicago, or -5
| [1] "1969-12-31 18:00:00 CST"
| R> as.numeric(timetest())
| [1] 0
| R> Sys.setenv("TZ"="Europe/London")
| R> timetest() # I can select another one
| [1] "1970-01-01 01:00:00 BST"
| R> Sys.setenv("TZ"="UTC")
| R> timetest() # incl UTC
| [1] "1970-01-01 UTC"
| R>
| R> format(timetest(), tz="America/Chicago")
| [1] "1969-12-31 18:00:00"
| R>
|
| So you need to change the timezone _at the level of your app_ which
can be
| as
| simple as writing a new Date formatter in R as per my last line.
|
| Dirk
|
| --
| http://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org
|
|
--
http://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org
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