Using Sugar Function all()

Ross Bennett — written Dec 23, 2012 — source

The sugar function all() answers the question, “Are all of the values … ?”.

The all_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 all() 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 all_sug(LogicalVector x) {
   // Note the use of is_true to return a bool type.
   return is_true(all(x == TRUE));
}

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

[1] TRUE

all_sug(x != 3)

[1] FALSE

all_sug(x >= y)

[1] TRUE

all_sug(y == 0)

[1] TRUE

While the above function may seem trivial, it can be easy to forget is_true() when using all() and will result in a compile error. The check_equal() function below is an example of a simple utility function to check two vectors for equality using the all_sug() function defined above.

// [[Rcpp::export]]
void check_equal(NumericVector x, NumericVector y) {
    if (all_sug(x == y)) {
	Rcout << "Success! The input vectors are equal" << std::endl;
	// do something
   } else {
	Rcout << "Fail! The input vectors are not equal" << std::endl;
	// do something else
   }
}

check_equal(x, y)

Fail! The input vectors are not equal

check_equal(x, c(3, 9, 0, 2, 7, 5, 6))

Success! The input vectors are equal

tags: sugar

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