How it works...

The sourcecpp function loads the C++ or Rcpp code from an external script and compiles it. In this C++ file, we first include the Rcpp headers that will allow us to add R functionality to our C++ script. We use using namespace Rcpp to tell the compiler that we want to work with that namespace (so we avoid the need to type Rcpp:: when using Rcpp functionality). The Rcpp::export declaration tells the compiler that we want to export this function to R.

Our bring_element function will return an integer (so that is why we have an int in its declaration). The arguments will be NumericVector and NumericMatrix, which are not C++ native variable types but Rcpp ones. These allow us to use vectors and matrices that operate with numbers without needing to declare explicitly if we will be working with integers, large integers, or float numbers. The Rcout function allows us to print output from C++ to the R console. We then loop through the columns and rows from the vector and the matrix, using standard C++ syntax. What is not standard here is the way we can get the number of columns and rows in these elements (using .rows() and .cols()), since these attributes are available through Rcpp. The R code is quite straightforward, and we then run it using a standard timer.