Hi List Members I have data stored in an matrix. Now, i want to acces the data of the matrix row-wise. because i want to access it in a sorted manner (without moving the matrix entries around), i make a stl-vector of matrix_rows. This works fine. But if i now use the stl algorithms to sort the stl-vector by a certain criteria, then it happens, that the algorithm is making several copies of a singe vector entry and overwriting other entries. Can anyone give me a tipp, what i'm doing wrong? ---------------------------- Here is an example code: #include<iostream> #include<vector> #include<algorithm> #include<cmath> #include #include namespace num=boost::numeric::ublas; template <int N> class Ordering { public: bool operator()(num::matrix_row A, num::matrix_row B) { if (A(N) < B(N) ) return true; else return false; } }; int main(int argc, char* argv[]) { const int N = 10000; const int M = 4; num::matrix<double> Matrix(N, M); for (int i = 0; i < Matrix.size1(); i++) { for (int j = 0; j < Matrix.size2(); j++) { Matrix(i, j) = drand48(); } } std::vector > MyAccess; for (int i = 0; i < Matrix.size1(); i++) { MyAccess.push_back(num::matrix_row(Matrix, i) ); } for (int i = 0; i < Matrix.size1(); i++) { std::cout << MyAccess[i] << std::endl; } std::sort(MyAccess.begin(), MyAccess.end(), Ordering<0>() ); for (int i = 0; i < Matrix.size1(); i++) { std::cout << MyAccess[i] << std::endl; } }