RcppResultSet {Rcpp} | R Documentation |
RcppResultSet
is a C++ class defined in Rcpp.h
that can
assign any number of C++ objects to R in a single named list object
as the SEXP
return value of a .Call()
function call.
The C++ objects can be of different types that are limited to
types double
, int
, string
, vectors of
double
or int
(with explicit dimensions),
matrices of double
or int
(with explicit dimensions),
STL vectors of double
, int
or string
, STL
‘vector of vectors’ of types double
or int
(all
with implicit dimensions), the internal types RcppDate
, RcppDateVector
,
RcppStringVector
, RcppVector
of types double
or
int
, RcppMatrix
of types double
or int
as well RcppFrame
, a type that can be converted into a
data.frame
, and the R type SEXP
.
Where applicable, the C++
types are automatically converted to the
corresponding R types structures around types numeric
,
integer
, or character
. The C++
code can all be
retrieved in R as elements of a named list object.
Usage of RcppResultSet
from C++
is fully defined in
Rcpp.h
. An example for returning data to R at the end of a
.Call()
call follows.
At the C++ level, the corresponding code to assign these parameter to
C++ objects is can be as follows (taken from the C++ source of
RcppExample
):
SEXP rl; RcppResultSet rs; rs.add("date", aDate); // RcppDate rs.add("dateVec", dateVec); // RcppDateVec rs.add("method", method); // string rs.add("tolerance", tol); // numeric rs.add("maxIter", maxIter); // int rs.add("matD", matD); // RcppMatrix rs.add("stlvec", stlvec); // vector<double> or <int> rs.add("stlmat", stlmat); // vector< vector <double> > // or <int> rs.add("a", a, nrows, ncols); // double** (or int**) with // two dimension rs.add("v", v, len); // double* (or int*) with // one dimension rs.add("stringVec", strVec); // RcppStringVector rs.add("strings", svec); // vector<string> rs.add("InputDF", inframe); // RcppFrame rs.add("PreDF", frame); // RcppFrame rl = rs.getReturnList(); return(rl);
As the R level, we assign the returned object a list variables from which we select each list element by its name. lookup is driven by the names givem at the R level, order is not important. It is however important that the types match. Errors are typically caught and an exception is thrown.
The class member function checkNames
can be used to verify that the
SEXP
object passed to the function contains a given set of
named object.
Dominick Samperi wrote most of Rcpp during 2005 and 2006. Dirk Eddelbuettel made some additions, and became maintainer in 2008.
RcppExample
, the vignette “RcppAPI”.
# example from RcppDate # set up date and datetime vectors dvec <- Sys.Date() + -2:2 dtvec <- Sys.time() + (-2:2)*0.5 # call the underlying C++ function result <- RcppDateExample(dvec, dtvec) # inspect returned object result