(C++) AllAboutEqual

August 30, 2019 · View on GitHub

AllAboutEqual is a std::vector checking

code snippet to check if all doubles in a std::vector are about equal.

#include <algorithm> #include <cassert> #include <functional> #include <vector> #include <boost/numeric/conversion/cast.hpp> ///fuzzy_equal_to is a predicate to test two doubles for equality ///with a certain tolerance. A tolerance of 0.0 denotes that ///an exact match is requested. Note that the value of 0.0 cannot ///be compared fuzzily. struct fuzzy_equal_to : public std::binary_function<double,double,bool> {   fuzzy_equal_to(const double tolerance = 0.01)     : m_tolerance(tolerance)   {     assert(tolerance >= 0.0);   }   bool operator()(const double lhs, const double rhs) const   {     const double d = std::abs(m_tolerance * lhs);     return rhs > lhs - d         && rhs < lhs + d;   }   const double m_tolerance; }; ///AllAboutEqual tests if all values in a std::vector are about equal. ///From http://www.richelbilderbeek.nl/CppAllAboutEqual.htm bool AllAboutEqual(   const std::vector<double>& v,   const double tolerance = 0.01) {   assert(!v.empty());   return std::count_if(     v.begin(),     v.end(),     std::bind2nd(fuzzy_equal_to(tolerance),v[0]))     == boost::numeric_cast<int>(v.size()); } int main() {   //C++11 initializer list   assert( AllAboutEqual( {  0.999,  1.0,  1.001  } ));   assert( AllAboutEqual( { -0.999, -1.0, -1.001  } ));   assert(!AllAboutEqual( {  0.999, -1.0, -1.001  } ));   assert(!AllAboutEqual( { -0.999,  1.0, -1.001  } ));   assert(!AllAboutEqual( { -0.999, -1.0,  1.001  } ));   assert(!AllAboutEqual( {  0.98 ,  1.0,  1.02   } ));   assert(!AllAboutEqual( {  0.9  ,  1.0,  1.1    } )); }