libigl/include/igl/median.cpp

// This file is part of libigl, a simple c++ geometry processing library.
//
// Copyright (C) 2013 Alec Jacobson <[email protected]>
//
// This Source Code Form is subject to the terms of the Mozilla Public License
// v. 2.0. If a copy of the MPL was not distributed with this file, You can
// obtain one at http://mozilla.org/MPL/2.0/.
#include "median.h"
#include "matrix_to_list.h"

#include <vector>
#include <algorithm>

template <typename DerivedV, typename mType>
IGL_INLINE bool igl::median(
  const Eigen::MatrixBase<DerivedV> & V, mType & m)
{
  if(V.size() == 0)
  {
    return false;
  }
  std::vector<typename DerivedV::Scalar> vV;
  matrix_to_list(V,vV);
  // http://stackoverflow.com/a/1719155/148668
  size_t n = vV.size()/2;
  std::nth_element(vV.begin(),vV.begin()+n,vV.end());
  if(vV.size()%2==0)
  {
    std::nth_element(vV.begin(),vV.begin()+n-1,vV.end());
    m = 0.5*(vV[n]+vV[n-1]);
  }else
  {
    m = vV[n];
  }
  return true;
}

#ifdef IGL_STATIC_LIBRARY
// Explicit template instantiation
// generated by autoexplicit.sh
template bool igl::median<Eigen::Block<Eigen::Matrix<float, -1, -1, 0, -1, -1>, -1, 1, true>, float>(Eigen::MatrixBase<Eigen::Block<Eigen::Matrix<float, -1, -1, 0, -1, -1>, -1, 1, true> > const&, float&);
// generated by autoexplicit.sh
template bool igl::median<Eigen::Block<Eigen::Matrix<double, -1, -1, 0, -1, -1>, -1, 1, true>, double>(Eigen::MatrixBase<Eigen::Block<Eigen::Matrix<double, -1, -1, 0, -1, -1>, -1, 1, true> > const&, double&);
template bool igl::median<Eigen::Matrix<double, -1, 1, 0, -1, 1>, double>(Eigen::MatrixBase<Eigen::Matrix<double, -1, 1, 0, -1, 1> > const&, double&);
#endif