Sort a RowXpr or ColXpr in Eigen 2.0.15

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someguy Registered Member Posts 14 Karma 0	Sort a RowXpr or ColXpr in Eigen 2.0.15 Wed Feb 16, 2011 8:10 pm Hi, How can I sort a row of a matrix? I tried used the function below, but it gets a lot of errors Thanks Code: Select all // Compile with g++ -c -I./eigen test_eigen.cpp #include <algorithm> #include <Eigen/Core> #include <Eigen/Array> USING_PART_OF_NAMESPACE_EIGEN typedef Eigen::Matrix<double, Eigen::Dynamic, Eigen::Dynamic> EigenMatrixDbl; template <typename ScalarType, typename Derived> void Sort(Eigen::MatrixBase<Derived> &xValues) { std::sort(xValues.derived().data(), xValues.derived().data()+xValues.derived().size()); } int main(int argc, char** argv) { EigenMatrixDbl m; m << 1, 2, 3, 4, 5, 6, 7, 8, 9; EigenMatrixDbl::RowXpr first_row = m.row(0); Sort<double>(first_row); return 0; } In file included from /usr/include/c++/4.4/algorithm:62, from test_eigen.cpp:1: /usr/include/c++/4.4/bits/stl_algo.h: In function âvoid std::__insertion_sort(_RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = const double]â: /usr/include/c++/4.4/bits/stl_algo.h:2178: instantiated from âvoid std::__final_insertion_sort(_RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = const double]â /usr/include/c++/4.4/bits/stl_algo.h:5222: instantiated from âvoid std::sort(_RAIter, _RAIter) [with _RAIter = const double]â test_eigen.cpp:13: instantiated from âvoid Sort(Eigen::MatrixBase<OtherDerived>&) [with ScalarType = double, Derived = Eigen::Block<Eigen::Matrix<double, 10000, 10000, 2, 10000, 10000>, 1, 10000, 1, 32>]â test_eigen.cpp:26: instantiated from here /usr/include/c++/4.4/bits/stl_algo.h:2109: error: assignment of read-only location â __firstâ /usr/include/c++/4.4/bits/stl_algo.h: In function âvoid std::__unguarded_linear_insert(_RandomAccessIterator, _Tp) [with _RandomAccessIterator = const double, _Tp = double]â: /usr/include/c++/4.4/bits/stl_algo.h:2112: instantiated from âvoid std::__insertion_sort(_RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = const double]â /usr/include/c++/4.4/bits/stl_algo.h:2178: instantiated from âvoid std::__final_insertion_sort(_RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = const double]â /usr/include/c++/4.4/bits/stl_algo.h:5222: instantiated from âvoid std::sort(_RAIter, _RAIter) [with _RAIter = const double]â test_eigen.cpp:13: instantiated from âvoid Sort(Eigen::MatrixBase<OtherDerived>&) [with ScalarType = double, Derived = Eigen::Block<Eigen::Matrix<double, 10000, 10000, 2, 10000, 10000>, 1, 10000, 1, 32>]â test_eigen.cpp:26: instantiated from here /usr/include/c++/4.4/bits/stl_algo.h:2069: error: assignment of read-only location â* __lastâ ...
ggael Moderator Posts 3447 Karma 19 OS	Re: Sort a RowXpr or ColXpr in Eigen 2.0.15 Wed Feb 16, 2011 9:48 pm in Eigen2 there is only a const version of the data() function, so instead you can use coeffRef: std::sort(&xValues.coeffRef(0), &xValues.coeffRef(0)+xValues.size());
someguy Registered Member Posts 14 Karma 0	Re: Sort a RowXpr or ColXpr in Eigen 2.0.15 Wed Feb 16, 2011 11:03 pm Thanks, but now the program segfaults! Code: Select all `template <typename ScalarType, typename Derived> void Sort(Eigen::MatrixBase<Derived> &xValues) { // std::sort(xValues.derived().data(), xValues.derived().data()+xValues.derived().size()); std::sort(&xValues.coeffRef(0), &xValues.coeffRef(0)+xValues.size()); }` Code: Select all `$ g++ -o test_eigen -I./eigen test_eigen.cpp && ./test_eigen Segmentation fault`
bjacob Registered Member Posts 658 Karma 3	Re: Sort a RowXpr or ColXpr in Eigen 2.0.15 Thu Feb 17, 2011 12:44 pm Compile with -g3 and get a backtrace! Join us on Eigen's IRC channel: #eigen on irc.freenode.net Have a serious interest in Eigen? Then join the mailing list!
Hauke Registered Member Posts 109 Karma 3 OS	Re: Sort a RowXpr or ColXpr in Eigen 2.0.15 Thu Feb 17, 2011 2:38 pm Since you are passing pointers to std::sort, the memory block must be continuous and neighboring elements must have a distance of 1 in ptr arithmetic. This is not the case for a row when Eigen is configured to work with column major memory layout. Or am I missing something? - Hauke
ggael Moderator Posts 3447 Karma 19 OS	Re: Sort a RowXpr or ColXpr in Eigen 2.0.15 Thu Feb 17, 2011 4:46 pm Yes Hauke is perfectly right.
someguy Registered Member Posts 14 Karma 0	Re: Sort a RowXpr or ColXpr in Eigen 2.0.15 Thu Feb 17, 2011 6:03 pm ggael wrote:Yes Hauke is perfectly right. OK, the question remains: how do I sort a RowXpr or ColXpr in Eigen 2.0.15? Thanks