犰狳中的Rcpp Sugar命令 [英] Rcpp sugar commands in armadillo

问题描述

我正在尝试将Rcpp sugar的 ifelse()命令与 arma :: vec 一起使用.代码失败并显示错误

I'm trying to use ifelse() command of Rcpp sugar with arma::vec. The code fails with error

'ifelse'

我找不到解决方案.下面是一个简单的示例代码(导致错误).

I could not find a solution. A simple example code (resulted with error) is below.

#include <RcppArmadillo.h>
// [[Rcpp::depends(RcppArmadillo)]]

// [[Rcpp::export]]
arma::vec f(arma::vec x, arma::vec y) {
  arma::vec res1 = Rcpp::ifelse(x < y, x, y);
  arma::vec res = trans(res1)*y;
  return res;
}

/*** R
f(c(1,2,3),c(3,2,1))
*/

推荐答案

使用Armadillo的高级构造函数您可以使 Rcpp :: NumericVector 和 arma :: vec 指向相同的内存位置.然后，可以通过使用该内存的正确前端对象来同时使用 Rcpp 函数和 arma 函数:

Using Armadillo's advanced constructors you can have Rcpp::NumericVector and arma::vec that refer to the same memory location. Then you can use both Rcpp functions and arma functions by using the correct front-end object for that piece of memory:

#include <RcppArmadillo.h>
// [[Rcpp::depends(RcppArmadillo)]]

// [[Rcpp::export]]
arma::vec f(Rcpp::NumericVector xr, Rcpp::NumericVector yr) {
  arma::vec x(xr.begin(), xr.size(), false, true); 
  arma::vec y(yr.begin(), yr.size(), false, true);
  Rcpp::NumericVector res1r(xr.size());
  arma::vec res1(res1r.begin(), res1r.size(), false, true);  
  res1r = Rcpp::ifelse(xr < yr, xr, yr);
  arma::vec res = trans(res1)*y;
  return res;
}

/*** R
f(c(1,2,3),c(3,2,1))
*/

我不是100％肯定它不会有任何不良副作用.

I am not 100% sure that this does not have any unwanted side-effects.

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