expandr.cpp

#include <Rcpp.h>
#include <string>
#include <sstream>

using namespace Rcpp;

//[[Rcpp::export]]

NumericMatrix expandR(CharacterVector x) {
    int n = x.size();
    std::vector< std::vector<int> > out;    // list to hold numeric vectors
    int tmax = 0;
    for(int i = 0; i < n; ++i) {
      std::vector<int> vect;                // vector to hold split strings
      std::string str = as<std::string>(x[i]);
      std::stringstream ss(str);
      int j = 0;
      while (ss >> j) {
      vect.push_back(j);  // add integer to result vector
        if (ss.peek() == ',') //split by ',' delim
          ss.ignore();
      }
     int it = *std::max_element(vect.begin(), vect.end());
      if( it > tmax )
        tmax = it;  //current max value
      out.push_back(vect);
    }
// Now we construct the matrix. tmax gives us number of columns, n is number of rows;
    NumericMatrix mat(n,tmax);
    for( int i = 0; i < n; ++i) {
      NumericMatrix::Row zzrow = mat( i , _ );
      std::vector<int> vec = out[i];
      for( int j = 0; j < vec.size(); ++j ) {
        zzrow[ (vec[j]-1) ] = 1; //don't forget R vs. C++ indexing
        }
    }
    return mat;
}