问题描述
到目前为止,我一直在尝试在Rcpp中实现apply函数,代码看起来像这样
I have been trying to implement apply function in Rcpp so far the code looks like this
//[[Rcpp::export]]
NumericVector apply(NumericMatrix x,int dim,Function f){
NumericVector output;
if(dim==1){
for(int i=0;i<x.nrow();i++){
output[i]=f(x(i,_));
}
}
else if(dim==2){
for(int i=0;i<x.ncol();i++){
output[i]=f(x(_,i));
}
}
return(output);
}
但是在第6行和第11行中出现错误无法将SEXP赋值转换为double值".是否有任何方法可以将任意函数返回的值转换为double?应用功能也有糖功能.
but i'm getting an error "cannot convert SEXP to double in assignment" in line 6 and 11. Is there any way to convert the value returned by an arbitrary function to double? also is there a sugar function for the apply function.
推荐答案
apply
没有糖功能.做您想做的最简单的方法是将 as< double>
称为,即:
There is no sugar function for apply
. The easiest way of doing what you want is to call as<double>
, i.e.:
output[i]=as<double>(f(x(i,_)));
您还可以将其嵌入一种可以为您调用 as
的类型,例如:
You could also embed this in a type that would call as
for you, something like:
template <typename T>
class F {
public:
F( SEXP f_) : f(f_){}
inline T operator()(NumericVector x){
return as<T>(f(x)) ;
}
private:
Function f ;
} ;
以便您可以执行以下操作:
so that you could do:
// [[Rcpp::export]]
NumericVector apply_cpp(NumericMatrix x,int dim,F<double> f){
if(dim==1){
NumericVector output(x.nrow());
for(int i=0;i<x.nrow();i++){
output[i]=f(x(i,_));
}
return output ;
}
else {
NumericVector output(x.ncol());
for(int i=0;i<x.ncol();i++){
output[i]=f(x(_,i));
}
return output ;
}
}
上面的 F
模板假定该函数采用 NumericVector
并返回可以转换为 double
的内容.您还可以嵌入有关输入和输出的类型信息.像这样的东西(在C ++ 11中表示):
The F
template from above assumes that the function takes a NumericVector
and returns something that can be converted to a double
. You could also embed type information about both inputs and outputs. Something like this (expressed in C++11):
template <typename T, typename... Args>
class F {
public:
F( SEXP f_) : f(f_){}
inline T operator()(Args... args){
return as<T>(f(args...)) ;
}
private:
Function f ;
} ;
然后签名将变为:
// [[Rcpp::export]]
NumericVector apply_cpp(NumericMatrix x,int dim,F<double,NumericVector> f){
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