为此，您应该可以使用arma::sort_index来实现，

You should be able to use arma::sort_index for this, which you mention in your post:

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

// [[Rcpp::export]]
arma::vec arma_sort(arma::vec x, arma::vec y) {
    return x(arma::sort_index(y));
}

/*** R
A <- c(0.5, 0.4, 0.2, 0.9)
B <- c(9, 1, 3, 5)
arma_sort(A, B)
*/

结果:

> arma_sort(A, B)
     [,1]
[1,]  0.4
[2,]  0.2
[3,]  0.9
[4,]  0.5

当然，还有其他方法.在纯C ++的上下文中，已经在Stack Overflow上对这个问题的变体进行了几次询问.下面，我在此处修改了Rcpp的答案:

Of course, there are other ways as well. Variations on this question have been asked a few times on Stack Overflow in the context of plain C++. Below I've adapted the answer here for Rcpp:

#include <Rcpp.h>

using namespace Rcpp;

// [[Rcpp::export]]
NumericVector Rcpp_sort(NumericVector x, NumericVector y) {
    // Order the elements of x by sorting y
    // First create a vector of indices
    IntegerVector idx = seq_along(x) - 1;
    // Then sort that vector by the values of y
    std::sort(idx.begin(), idx.end(), [&](int i, int j){return y[i] < y[j];});
    // And return x in that order
    return x[idx];
}

/*** R
A <- c(0.5, 0.4, 0.2, 0.9)
B <- c(9, 1, 3, 5)
Rcpp_sort(A, B)
*/

结果:

> Rcpp_sort(A, B)
[1] 0.4 0.2 0.9 0.5