Hi Andrew,
On 9 September 2010 at 08:52, Andrew Redd wrote:
| What is the appropriate way to use/convert named vectors in C++ with
| Rcpp. Basically I have a named vector of parameters that pass into
| the function. I cannot be certain of their order, so would like to
| extract them by name. For those initialized in C++ a
| std:map<std::string, double> should work, but how do declare one from
| a SEXP pointer that is passed in? For example:
|
| draw <- cxxfunction(signature(A="numeric",t="numeric",
params="numeric"),body="
| SEXP draw( SEXP A, SEXP t, SEXP params){
| Rcpp::NumericVector Admissions(A);
| Rcpp::NumericVector T(t);
| std::map<std::string, double> Params(params);
| std::vector<double> draws;
| for(int i=0;i<params[\"n\"];i++){
| draws.pushback(rbinom(Admissions[T[i]+1,2],
1/(1+exp(-params[\"nu\"])))));
| }
| return wrap(draws);
| }
| ",plugin='Rcpp')
| This of course does not compile because of std::map<std::string,
| double> Params(params); is not valid. But is shows more of less what
| I'm trying to do.
There is no explicit 'unrolling' of named vectors into maps. OTOH as<> works
over atomistic types that can be iterated, and we do talk about the opposite
way (using Rcpp::wrap) in the intro vignette. There may be something close
in the 700+ unit tests. Maybe we already can -- I just haven't tried.
I tend to pass named lists down from R and pick paraeters one-by-one out of
the Rcpp::List once in C++. Here is a working example from something Shane
and I working on:
R side:
val <- .Call("SVMregression",
X=x, y=y,
list(C=C,
gamma=gamma,
epsilon=epsilon,
sigma=sigma,
type=type,
kernel=kernel
),
PACKAGE="rshark")
C++ side:
RcppExport SEXP SVMregression(SEXP Xs, SEXP Ys, SEXP svmParameters) {
try {
Rcpp::NumericMatrix xR = Rcpp::NumericMatrix(Xs);
Rcpp::NumericVector yR = Rcpp::NumericVector(Ys);
Rcpp::List rparam(svmParameters);
double C = Rcpp::as<double>(rparam["C"]);
double epsilon = Rcpp::as<double>(rparam["epsilon"]);
double gamma = Rcpp::as<double>(rparam["gamma"]);
double sigma = Rcpp::as<double>(rparam["sigma"]);
string type = Rcpp::as<string>(rparam["type"]);
string kernel = Rcpp::as<string>(rparam["kernel"]);
I am happy with this as the lists typically contain different types (double,
string, bool, ...) anyway.
Does that help?
Dirk
--
Dirk Eddelbuettel | e...@debian.org | http://dirk.eddelbuettel.com
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