[英]Passing R functions to C routines using rcpp
I have a C function from a down-stream library that I call in C like this 我有一个来自下游库的C函数,我在C中调用这样的函数
result = cfunction(input_function)
input_function
is a callback that needs to have the following structure input_function
是一个需要具有以下结构的回调
double input_function(const double &x)
{
return(x*x);
}
Where x*x
is a user-defined computation that is usually much more complicated. 其中x*x
是用户定义的计算,通常要复杂得多。 I'd like to wrap cfunction
using Rcpp so that the R user could call it on arbitrary R functions. 我想使用Rcpp包装cfunction
以便R用户可以在任意R函数上调用它。
NumericVector rfunction(Function F){
NumericVector result(1);
// MAGIC THAT I DON'T KNOW HOW TO DO
// SOMEHOW TURN F INTO COMPATIBLE input_funcion
result[0] = cfunction(input_function);
return(result);
}
The R user then might do rfunction(function(x) {x*x})
and get the right result. 然后R用户可以执行rfunction(function(x) {x*x})
并获得正确的结果。
I am aware that calling R functions within cfunction
will kill the speed but I figure that I can figure out how to pass compiled functions later on. 我知道在cfunction
中调用R函数会降低速度,但我认为我可以弄清楚如何在以后传递编译函数。 I'd just like to get this part working. 我只想让这部分工作。
The closest thing I can find that does what I need is this https://sites.google.com/site/andrassali/computing/user-supplied-functions-in-rcppgsl which wraps a function that uses callback that has an oh-so-useful second parameter within which I could stuff the R function. 我能找到的最接近我需要的是这个https://sites.google.com/site/andrassali/computing/user-supplied-functions-in-rcppgsl ,它包含一个使用回调函数的函数非常有用的第二个参数,我可以填充R函数。
Advice would be gratefully received. 我们将非常感谢您的建议。
One possible solution would be saving the R-function into a global variable and defining a function that uses that global variable. 一种可能的解决方案是将R函数保存为全局变量并定义使用该全局变量的函数。 Example implementation where I use an anonymous namespace to make the variable known only within the compilation unit: 我使用匿名命名空间使变量只在编译单元中知道的示例实现:
#include <Rcpp.h>
extern "C" {
double cfunction(double (*input_function)(const double&)) {
return input_function(42);
}
}
namespace {
std::unique_ptr<Rcpp::Function> func;
}
double input_function(const double &x) {
Rcpp::NumericVector result = (*func)(x);
return result(0);
}
// [[Rcpp::export]]
double rfunction(Rcpp::Function F){
func = std::make_unique<Rcpp::Function>(F);
return cfunction(input_function);
}
/*** R
rfunction(sqrt)
rfunction(log)
*/
Output: 输出:
> Rcpp::sourceCpp('57137507/code.cpp')
> rfunction(sqrt)
[1] 6.480741
> rfunction(log)
[1] 3.73767
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