R Language Rcpp Rcpp Attributes
Example
Rcpp Attributes makes the process of working with R and C++ straightforward. The form of attributes take:
// [[Rcpp::attribute]]
The use of attributes is typically associated with:
// [[Rcpp::export]]
that is placed directly above a declared function header when reading in a C++ file via sourceCpp().
Below is an example of an external C++ file that uses attributes.
// Add code below into C++ file Rcpp_example.cpp
#include <Rcpp.h>
using namespace Rcpp;
// Place the export tag right above function declaration.
// [[Rcpp::export]]
double muRcpp(NumericVector x){
int n = x.size(); // Size of vector
double sum = 0; // Sum value
// For loop, note cpp index shift to 0
for(int i = 0; i < n; i++){
// Shorthand for sum = sum + x[i]
sum += x[i];
}
return sum/n; // Obtain and return the Mean
}
// Place dependent functions above call or
// declare the function definition with:
double muRcpp(NumericVector x);
// [[Rcpp::export]]
double varRcpp(NumericVector x, bool bias = true){
// Calculate the mean using C++ function
double mean = muRcpp(x);
double sum = 0;
int n = x.size();
for(int i = 0; i < n; i++){
sum += pow(x[i] - mean, 2.0); // Square
}
return sum/(n-bias); // Return variance
}
To use this external C++ file within R, we do the following:
require(Rcpp)
# Compile File
sourceCpp("path/to/file/Rcpp_example.cpp")
# Make some sample data
x = 1:5
all.equal(muRcpp(x), mean(x))
## TRUE
all.equal(varRcpp(x), var(x))
## TRUE
