Iterator for columns of matrix: copying matrix column to std::vector?

Question

Trying to return an std::vector from a designated column in a matrix. This is the code I have so far:

template <typename T>
vector<T> ExtractMatrixColAsVector(NumericMatrix x, NumericVector column){
  vector<T> values = as<vector<T> >(NumericVector(x(_,as<int>(column))));
  return values;
}

I was wondering whether there was a better way of doing this if I wanted to convert the whole matrix into separate vectors? Is there an iterator for this purpose or some syntactic sugar that returns a vector of that column automatically?

Thanks for any help.

Answer 1

You could use a quick for loop to convert the whole matrix.

// [[Rcpp::export]]
vector< vector<double> > ExtractMatrixAsVectors(NumericMatrix x){
  vector< vector<double> > values(x.nrow());
  for(int i=0; i<values.size(); i++) values[i] = as< vector<double> >(NumericVector(x(_,i)));
  return values;
}

Also, I don't see too much point in using a template. The output of a numeric matrix column will always be a double precision float.