Rcpp forbidden conversion when using any() in an if() statement - r

Question

I am trying to convert my R function to C++ using Rcpp, but I came around errors that I don't understand quite well.
The following code gives my R function, my (poor) attempt to translate it and some examples of uses at the end (testing that the two function return the same thing...)
My R Code function:
intersect_rectangles <- function(x_min, x_max, y_min, y_max) {
rez <- list()
rez$min <- pmax(x_min, y_min)
rez$max <- pmin(x_max, y_max)
if (any(rez$min > rez$max)) {
return(list(NULL))
}
return(rez)
}
My attempt to create the same function with Rcpp.
#include <Rcpp.h>
using namespace Rcpp;
// [[Rcpp::export]]
List Cpp_intersect_rectangles(NumericVector x_min,NumericVector
x_max,NumericVector y_min,NumericVector y_max) {
// Create a list :
NumericVector min = pmax(x_min,y_min);
NumericVector max = pmin(x_max,y_max);
List L = List::create(R_NilValue);
if (! any(min > max)) {
L = List::create(Named("min") = min , _["max"] = max);
}
return(L);
}
I receive the following error messages:
/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/sugar/logical/SingleLogicalResult.h:36:2: error: implicit instantiation of undefined template 'Rcpp::sugar::forbidden_conversion<false>'
forbidden_conversion<x>{
^
/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/sugar/logical/SingleLogicalResult.h:74:40: note: in instantiation of template class 'Rcpp::sugar::conversion_to_bool_is_forbidden<false>' requested here
conversion_to_bool_is_forbidden<!NA> x ;
^
file637e53281965.cpp:13:9: note: in instantiation of member function 'Rcpp::sugar::SingleLogicalResult<true, Rcpp::sugar::Negate_SingleLogicalResult<true, Rcpp::sugar::Any<true, Rcpp::sugar::Comparator<14, Rcpp::sugar::greater<14>, true, Rcpp::Vector<14, PreserveStorage>, true, Rcpp::Vector<14, PreserveStorage> > > > >::operator bool' requested here
if (! any(min > max))
If the Rcpp function is implemented correctly, then the following should work:
u = rep(0,4)
v = rep(1,4)
w = rep(0.3,4)
x = c(0.8,0.8,3,3)
all.equal(intersect_rectangles(u,v,w,x), Cpp_intersect_rectangles(u,v,w,x))
all.equal(intersect_rectangles(u,v,w,w), Cpp_intersect_rectangles(u,v,w,w))
What's wrong with my cpp code?

Answer 1

The reason the code isn't translating correctly is due to how the any() Rcpp sugar implementation was created. In particular, we have that:
The actual return type of any(X) is an instance of the
SingleLogicalResult template class, but the functions is_true
and is_false may be used to convert the return value to bool.
Per https://thecoatlessprofessor.com/programming/unofficial-rcpp-api-documentation/#any
Therefore, the solution is to add .is_true() to the any() function call, e.g. !any(condition).is_true().
#include <Rcpp.h>
using namespace Rcpp;
// [[Rcpp::export]]
List Cpp_intersect_rectangles(NumericVector x_min, NumericVector x_max,
NumericVector y_min, NumericVector y_max) {
// Create a list :
NumericVector min = pmax(x_min, y_min);
NumericVector max = pmin(x_max, y_max);
List L = List::create(R_NilValue);
if (! any(min > max).is_true()) {
// ^^^^^^^^^ Added
L = List::create(Named("min") = min , _["max"] = max);
}
return(L);
}
Then, through testing we get:
u = rep(0,4)
v = rep(1,4)
w = rep(0.3,4)
x = c(0.8,0.8,3,3)
all.equal(intersect_rectangles(u,v,w,x), Cpp_intersect_rectangles(u,v,w,x))
# [1] TRUE
all.equal(intersect_rectangles(u,v,w,w), Cpp_intersect_rectangles(u,v,w,w))
# [1] TRUE