useful functions in Rcpp

RcppFns.cpp

/* the "vals" part of R's rle (run-length encoding) */
Rcpp::IntegerVector rle_vals(const Rcpp::IntegerVector& x){

  int n = x.size();

  /* y */
  Rcpp::IntegerVector head = x[Rcpp::seq(1,n-1)];
  Rcpp::IntegerVector tail = x[Rcpp::seq(0,n-2)];
  Rcpp::LogicalVector y = head != tail;

  /* i */
  Rcpp::IntegerVector y_ix  = Rcpp::seq(0,y.size()-1);
  y_ix = y_ix[y];
  y_ix.push_back(n-1);

  return x[y_ix];
}