Question

我正在Rccp和Rcpparmadillo中开发一个交叉验证循环。相同的循环在R中可以完美地工作。问题在于，在Rcpp中，循环的旧值不会被丢弃。下面是一个非常简化的代码。 frmwC是一个很大的Rcpparmadillo函数，当迭代次数为1（nR）时，R函数具有相同的结果，但是当nR较大时，会将先前的值添加到新值中，但是我想保留最后一个值就像R中发生的那样。frmwC将结果导出为列表

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以下是nR = 1的结果

#include <RcppArmadillo.h>
// [[Rcpp::depends(RcppArmadillo)]]
using namespace Rcpp;
using namespace arma;

// [[Rcpp::export()]]
mat mult(const mat& X,const mat& Y, const mat& Xt, IntegerVector idx, int A, int nR) 
{
  uvec idx1 = as<uvec>(idx);
  List model;
  NumericMatrix Yc1;

  for (int i = 0; i <nR; i++)
  {
     mat X0 = X.rows(idx1);
     mat Y0 = Y.rows(idx1);
     mat X1 = subset_mat(X, idx);
     mat Y1 = subset_mat(Y, idx);
     // Rcout << X0;
     model = frmwC(X1,Y1,X0, A = A);
  }

  mat Yc = as<mat>(model("predYt"));
  return Yc;
}

nR = 10的结果

X = matrix(runif(100, 1, 100),10,10)
Y = matrix(round(runif(10,1,100)))
Xt = matrix(runif(50,1,100),5,10)
Yt = matrix(round(runif(5, 1,100)))
idx = sample(size = 5, 0:9)
A = 10; nR = 1; nG = 2; Ix = matrix(0, A, ncol(X) + 1)

mult(X = X, Y = Y, Xt, idx = idx, A = A, nR = nR)

         [,1]     [,2]     [,3]     [,4]     [,5] [,6] [,7] [,8] [,9] [,10]
[1,] 61.28675 80.15003 76.19408 73.11867 72.55760    0    0    0    0     0
[2,] 48.45832 43.98474 36.04582 33.73255 32.79945    0    0    0    0     0
[3,] 35.35432 32.30002 37.16849 39.35326 39.58430    0    0    0    0     0
[4,] 54.93001 48.29227 44.68769 53.29742 53.36127    0    0    0    0     0
[5,] 52.17147 64.95472 65.61675 76.79194 75.09447    0    0    0    0     0

并使用R版本的代码

         [,1]     [,2]     [,3]     [,4]     [,5] [,6] [,7] [,8] [,9] [,10]
[1,] 714.3052 733.1685 729.2125 726.1371 725.5760    0    0    0    0     0
[2,] 343.6533 339.1798 331.2408 328.9276 327.9945    0    0    0    0     0
[3,] 391.6130 388.5587 393.4271 395.6119 395.8430    0    0    0    0     0
[4,] 535.1815 528.5437 524.9391 533.5489 533.6127    0    0    0    0     0
[5,] 728.0217 740.8049 741.4669 752.6421 750.9447    0    0    0    0     0

只要idx相同，则所有值（无论迭代应相同）都相同。如何使Rcpp放弃循环中的先前值并仅保留最后一个？我的交叉验证更加复杂，我不能只将值除以迭代次数。谢谢你

Answer 1

我终于解决了问题所在的问题，在frmwC函数中声明了矩阵的初始化。最初，我没有声明初始值，这导致了问题。现在我声明了一个初始值，并且一切都按预期进行（请检查下面的代码脚本。但是我不确定为什么会这样。如果有人能够详细说明，那将是完美的

mat T = zeros(X.n_rows, A), P = zeros(X.n_cols, A), V = P, W = P,
    B = zeros(X.n_cols, Y.n_cols), Q = zeros(Y.n_cols, A), 
    Ys = zeros(X.n_rows, A-1),
    Yts = zeros(Xt.n_rows, A), Si = zeros(X.n_cols, X.n_cols), 
    Bt = zeros(X.n_cols, A),Xi = zeros(X.n_cols, X.n_rows),
    Res = zeros(A, 6), Cor = zeros(A,1);

Rccp循环功能不会放弃旧值

1 个答案: