constructing a Data Frame in Rcpp

Question

I want to construct a data frame in an Rcpp function, but when I get it, it doesn\'t really look like a data frame. I\'ve tried pushing vectors etc. but it leads to the same

Answer 1

Using the information from @baptiste's answer, this is what finally does give a well formed data frame:

RcppExport SEXP makeDataFrame(SEXP in) {
    Rcpp::DataFrame dfin(in);
    Rcpp::DataFrame dfout;
    Rcpp::CharacterVector namevec;
    std::string namestem = "Column Heading ";
    for (int i=0;i<2;i++) {
        dfout.push_back(dfin(i));
        namevec.push_back(namestem+std::string(1,(char)(((int)'a') + i)));
    }
    dfout.attr("names") = namevec;
    Rcpp::DataFrame x;
    Rcpp::Language call("as.data.frame",dfout);
    x = call.eval();
    return x;
}

I think the point remains that this might be inefficient due to push_back (as suggested by @Dirk) and the second Language call evaluation. I looked up the rcpp unitTests, and haven't been able to come up with something better yet. Anybody have any ideas?

Update:

Using @Dirk's suggestions (thanks!), this seems to be a simpler, efficient solution:

RcppExport SEXP makeDataFrame(SEXP in) {
    Rcpp::DataFrame dfin(in);
    Rcpp::List myList(dfin.length());
    Rcpp::CharacterVector namevec;
    std::string namestem = "Column Heading ";
    for (int i=0;i