Example of using the Rcpp sugar function any()

2012-12-23-sugar-any.cpp

/**
 * @title Using Sugar Function any()
 * @author Ross Bennett
 * @license GPL (>= 2)
 * @tags sugar, any
 * @summary Illustrates the use of sugar function any()
 *
 * The sugar function any() answers the question, "Are any of the values ... ?".
 * 
 */
 
/**
 * The any_sug() function takes a LogicalVector as an argument and allows one to
 * enter an expression for the argument as shown in the R examples. In this example,
 * it is simply wrapper around the sugar function any() and includes is_true to
 * return a boolean.
 * Note that when comparing two vectors, it is an element-wise comparison.
 * (i.e. x[0] > y[0], ..., x[n] > y[n])
 */
 
#include <Rcpp.h>
using namespace Rcpp;

// [[Rcpp::export]]
bool any_sug(LogicalVector x){
	// Note the use of is_true to return a bool type
	return is_true(any(x == TRUE));
}
 
/**
 * While the above function may seem trivial, it can be easy to forget is_true() when
 * using any() and will result in a compile error. The check_negative() function below
 * is an example of a simple utility function to check if a vector contains negative values
 * using the any_sug() function defined above. 
 */
 
// [[Rcpp::export]]
void check_negative(NumericVector x) {
	if(any_sug(x < 0)) {
		std::cout << "The vector contains negative numbers" << std::endl;
		// do something
	} else {
		std::cout << "The vector does not contain negative numbers" << std::endl;
		// do something else
	}
}
 
/*** R
 x <- c(3, 9, 0, 2, 7, -1, 6)
 y <- c(8, 3, 2, 6, 1, 5, 0)
 any_sug(x < 10)
 any_sug(x != 3)
 any_sug(x >= y)
 any_sug(y == 0)
 check_negative(x)
 check_negative(y)
 */