Using Sugar Function any()

Ross Bennett — written Dec 23, 2012 — source

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));
}

 x <- c(3, 9, 0, 2, 7, -1, 6)
 y <- c(8, 3, 2, 6, 1, 5, 0)
 any_sug(x < 10)

[1] TRUE

 any_sug(x != 3)

[1] TRUE

 any_sug(x >= y)

[1] TRUE

 any_sug(y == 0)

[1] 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)) {
      Rcout << "The vector contains negative numbers" << std::endl;
      // do something
   } else {
      Rcout << "The vector does not contain negative numbers" << std::endl;
      // do something else
   }
}

check_negative(x)

The vector contains negative numbers

check_negative(y)

The vector does not contain negative numbers

tags: sugar

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