On Sat, 3 Apr 2021 at 16:28, prezzemolo <prezzem...@ctemplar.com> wrote:
>
> Hey.
>
> I am wondering if there's some general guidance on what the 'right' options
> are to cleanly handle character arguments passed from R to Rcpp.
>
> It is all rather simple: let's say I have a human-readable argument vector
> c("tree", "herb", "shrub") [It could also be a factor in R], which I can send
> to an Rcpp function along with other arguments for evaluation.
> What would be the cleanest way to define those arguments (plant types) in R
> to then have as little trouble sending them over to Rcpp for use in cases
> like if() statements?
You can use the == operator with standard strings:
Rcpp::cppFunction('
void test(std::string x) {
if (x == "flower")
Rcout << "flower" << std::endl;
else if (x == "tree")
Rcout << "tree" << std::endl;
else
Rcout << "string " << x << " not found" << std::endl;
}
')
test("flower")
#> flower
test("tree")
#> tree
test("other")
#> string other not found
Iñaki
>
>
> The use of enums comes to mind:
>
> // beginningoffile
> enum class var_type { flower, tree };
>
> RCPP_EXPOSED_ENUM_NODECL(var_type)
>
> // [[Rcpp::export]]
> int charHandle1(var_type text_arg = var_type::flower) {
> if(text_arg == var_type::flower) {
> Rcout << static_cast<int>(text_arg) << " says '0 (flower)'.\n";
> } else if(text_arg == var_type::tree) {
> Rcout << static_cast<int>(text_arg) << " says '1 (tree)'.\n";
> }
> return 0;
> }
> // endoffile
>
> This however, doesn't seem to work. I understand R would have to know the
> var_type for it to work.
> Then I can do it simply by comparing the const char * argument. This will
> work, but the strcmp() comparison isn't very straightforward for someone who
> doesn't know C++ (and perhaps for some other reasons).
>
> // [[Rcpp::export]]
> int charHandle2(const char* text_arg = "flower") {
> if(strcmp(text_arg, "flower") == 0) {
> Rcout << text_arg << " says 'flower'.\n";
> } else if(strcmp(text_arg, "tree") == 0) {
> Rcout << text_arg << " says 'tree'.\n";
> }
> return 0;
> }
>
> I am looking for some good practice guidance on how to handle this safely and
> legibly to avoid sending people to function definitions. An argument could be
> made, for instance, that a list of plant type used as function arguments
> could be stored as factor in R and then sent and used in some way in Rcpp.
> What other options are there? To my best knowledge, support for enums is
> limited - I glanced over the vignettes and couldn't find any significant
> mention of enums (or factors, really), so I guess some other way of handling
> such cases should be taken. Has anyone dealt with such cases and has
> recommendations?
>
> Regards,
> Angelo (Greetings from Genoa)
> _______________________________________________
> Rcpp-devel mailing list
> Rcpp-devel@lists.r-forge.r-project.org
> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
--
Iñaki Úcar
_______________________________________________
Rcpp-devel mailing list
Rcpp-devel@lists.r-forge.r-project.org
https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
