Some sample Rcpp code

rcpp_examples.R

library(Rcpp)

# Simple addition
add_r <- function(x, y, z) {
  sum = x + y + z
  return(sum)
}

cppFunction(
  "int add_c(int x, int y, int z) {
    int sum = x + y + z;
    return sum;
  }")

add_r(1, 2, 3)
add_c(1, 2, 3)

# Euclidean distance
dist_r <- function(x, ys) {
  sqrt((x - ys) ^ 2)
}

cppFunction(
  "NumericVector dist_c(double x, NumericVector ys) {
    int n = ys.size();
    NumericVector out(n);
  
    for(int i = 0; i < n; i++) {
      out[i] = sqrt(pow(ys[i] - x, 2.0));
    }
    return out;
  }")

dist_r(10, 20:25)
dist_c(10, 20:25)

# Summation with conditionals
sum_r <- function(v) {
  total <- 0
  for (e in v) {
    if (e < 0) { total = total - e }
    else if (e > 0.75) { total = total + e/2 }
    else { total = total + e }
  }
  
  return(total)
}

cppFunction(
  "double sum_c(NumericVector v) {
    double total = 0;
    for (int i = 0; i < v.size(); i++) {
      if (v[i] < 0) { total -= v[i]; }
      else if (v[i] > 0.75) { total += v[i]/2; }
      else { total += v[i]; }
    }

    return(total);
  }")

v <- runif(100000, -1, 1)
microbenchmark::microbenchmark(sum_r(v), sum_c(v))