fix an issue in mlpack decision tree

orderTheLabels.cpp

#include <iostream>
#include "armadillo"

using namespace arma;
using namespace std;

/*
 *This one will output " 3        1        2        9        0        1        8        2        5"
 */
int test1() {
        arma::Mat<double> labels = {"2 1 5 3 8 9 2 0 1"};
        arma::uvec sortedIndices = arma::sort_index(labels);
        arma::Row<size_t> sortedLabels(labels.n_elem);
        for (size_t i = 0; i < sortedLabels.n_elem; ++i)
                sortedLabels[sortedIndices[i]] = labels[i];
        std::cout <<  sortedIndices << std::endl;
        std::cout << '\n' << std::endl;
        std::cout <<  sortedLabels << std::endl;
        return 0;
}

/*
 *This one will output " 0        1        1        2        2        3        5        8        9" which is right(I think :))
 */

int test2() {
        arma::Mat<double> labels = {"2 1 5 3 8 9 2 0 1"};
        arma::uvec sortedIndices = arma::sort_index(labels);
        arma::Row<size_t> sortedLabels(labels.n_elem);
        for (size_t i = 0; i < sortedLabels.n_elem; ++i)
                sortedLabels[i] = labels[sortedIndices[i]];
        std::cout <<  sortedIndices << std::endl;
        std::cout << '\n' << std::endl;
        std::cout <<  sortedLabels << std::endl;
        return 0;
}