[Rcpp-devel] Named vectors
Dirk Eddelbuettel
edd at debian.org
Thu Sep 9 18:09:56 CEST 2010
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 were numerous other errors I fixed:
1) Do not add a function header as inline does that for you.
2) Do not add a final } either.
3) Your Params can be passed to a list as I showed.
4) I do not understand what Admissions[T[i]+1,2] could possible do for a
NumericVector Admissions. Did you mean a matrix? Changed to vector.
5) rbinom is now defined in SVN (wait for 0.8.6 "soon"). I presume you meant
the function from R itself returning a double so I changed that with
explicit prefixes.
So this now builds for me:
> draw <- cxxfunction(signature(A="numeric",t="numeric", params="numeric"),body="
+ Rcpp::NumericVector Admissions(A);
+ Rcpp::NumericVector T(t);
+ Rcpp::List Params(params);
+ int len = Rcpp::as<int>(Params[\"n\"]);
+ Rcpp::NumericVector draws(len);
+ for(int i=0; i<len; i++){
+ draws[i] = ::Rf_rbinom(Admissions[T[i]], 1/(1+exp(-Rcpp::as<double>(Params[\"nu\"]))));
+ }
+ return draws;
+ ",plugin='Rcpp')
>
We don;t need the Rcpp:: prefixes but I like'em too.
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