no matching function for call in rcpp - c++

Question

When using Rcpp,I create a function named rpois_rcpp and l try to call it below in genDataList function, an error occurs and said :
"no matching function for call to 'cpprbinom',
candidate function not viable: no known conversion from 'arma::vec' (aka 'Col') to 'Rcpp::NumericVector' (aka 'Vector<14>') for 3rd argument
arma::vec cpprbinom(int n, double size, NumericVector prob).
Can someone help me ,thanks!
Here is my code:
//create a random matrix X with covariance matrix sigma
// [[Rcpp::export]]
arma::mat mvrnormArma(const int n, arma::vec mu, const int p, const
double rho) {
arma::mat sigma(p, p, arma::fill::zeros);
for (int i = 0; i < sigma.n_rows; ++i) {
for (int j = 0; j < sigma.n_cols; ++j) {
sigma(i,j) = pow(rho, abs((i + 1) - (j + 1)));
}
}
int ncols = sigma.n_cols;
arma::mat Y = arma::randn(n, ncols);
return arma::repmat(mu, 1, n).t() + Y * arma::chol(sigma);
}
//create a vector sampled from poisson distribution with mean vector
//lambda
// [[Rcpp::export]]
arma::vec rpois_rcpp( NumericVector &lambda) {
int n= lambda.length();
unsigned int lambda_i = 0;
IntegerVector sim(n);
for (unsigned int i = 0; i < n; i++) {
sim[i] = R::rpois(lambda[lambda_i]);
// update lambda_i to match next realized value with correct mean
lambda_i++;
}
return as<arma::vec>(sim);
}
//create a vector sampled from binomial distribution with probability
vector prob
// [[Rcpp::export]]
arma::vec cpprbinom(int n, double size, NumericVector prob) {
NumericVector v = no_init(n);
std::transform( prob.begin(), prob.end(), v.begin(), [=](double p){
return R::rbinom(size, p); });
return as<arma::vec>(v);}
// [[Rcpp::export]]44
List genDataList(int n, arma::vec& mu, int p, double rho,
arma::vec& beta, const double SNR, const std::string &
Test_case) {
arma::mat U, V, data, normData, Projection;
arma::vec s, y, means, noise;
data = mvrnormArma(n, mu, p, rho);
normData = arma::normalise(data,2,0);
arma::svd_econ(U,s,V,normData,"right");
Projection = V * trans(V);
beta = Projection * beta;
if(Test_case == "gaussian")
{
means=normData * beta;
y = means + arma::randn(n) * sqrt(arma::var(means) / SNR);}
else if (Test_case == "poisson")
{
means=exp(normData * beta);
y = rpois_rcpp(means);}
else
{
means=exp(normData * beta)/(1 + exp(normData * beta));
y = cpprbinom(n,1,means);}
List ret;
ret["data"] = data;
ret["normData"] = normData;
ret["V"] = V;
ret["beta"] = beta;
ret["y"] = y;
return ret;
}

Answer 1

Thanks for adding your code. When I tried to compile, I got the same error as you, but also an error for the line calling rpois_rcpp()
invalid initialization of reference to type 'Rcpp::NumericVector&'
Pretty much everything seems to be in arma, except the R bindings and calls to the R:: namespace, which takes doubles, ints, etc. It seems the easiest thing to do (to my mind), is just take arma::vec as arguments instead:
arma::vec rpois_rcpp( arma::vec &lambda) {
int n= lambda.n_elem;
and
arma::vec cpprbinom(int n, double size, arma::vec prob) {
You never utilize the fact that lambda and prob are Rcpp::NumericVectors specifically, you just use doubles from them, so this seems the easiest route to me. After those changes, your code compiles fine on my machine. I don't have any test cases to make sure they run as you'd expect, but I imagine they will.