Technical facts

Operating system(s) or programming environment(s)

Lubuntu 15.04 (vivid)

IDE(s):

Qt Creator 3.1.1

Project type:

Console application

C++ standard:

C++11

Compiler(s):

G++ 4.9.2

Libraries used:

STL: GNU ISO C++ Library, version 4.9.2

Qt project file: ./CppMultimapToMap/CppMultimapToMap.pro


TEMPLATE = app

CONFIG += console

CONFIG -= app_bundle

CONFIG -= qt

QMAKE_CXXFLAGS += -std=c++11 -Wall -Wextra -Werror

SOURCES += main.cpp

./CppMultimapToMap/main.cpp


#include <cassert>

#include <map>



template <class Key, class Value>

const std::map<Key,Value> MultimapToMap(

  const std::multimap<Key,Value> m)

{

  std::map<Key,Value> n;

  const auto end = m.end();

  for (auto begin = m.begin(); begin != end; )

  {

    assert(begin != m.end());

    const auto key = (*begin).first;

    assert(m.find(key) != m.end());



    //Must the average be calculated?

    const auto r = m.equal_range(key);

    assert(r.first != m.end());



    if (r.first != r.second )

    {

      Value sum(0.0);

      int cnt = 0;

      for (auto i = r.first; i!=r.second; ++i)

      {

        sum += (*i).second;

        ++cnt;

      }

      const Value result( sum / static_cast<double>(cnt));

      n[ key ] = result;

    }

    else

    {

      const Value result((*r.first).second);

      n[ key ] = result;

    }

    begin = r.second;

  }

  return n;

}



int main()

{

  {

    const std::multimap<int,double> m ( { { 1, 1.0} } );

    const std::map<int,double> n(MultimapToMap(m));

    assert(n.size() == 1);

  }

  {

    const std::multimap<int,double> m ( { { 1, 1.0}, { 1, 1.0} } );

    const std::map<int,double> n(MultimapToMap(m));

    const std::map<int,double> e( { { 1, 1.0 } } );

    assert(n.size() == 1);

    assert(n == e);

  }

  {

    const std::multimap<int,double> m ( { { 1, 1.0}, { 1, 2.0} } );

    const std::map<int,double> n(MultimapToMap(m));

    const std::map<int,double> e( { { 1, 1.5 } } );

    assert(n.size() == 1);

    assert(n == e);

  }

  {

    const std::multimap<int,double> m ( { {0, 0.0}, { 1, 1.0}, { 1, 1.0}, {2, 2.0} } );

    const std::map<int,double> n(MultimapToMap(m));

    const std::map<int,double> e( { {0, 0.0}, { 1, 1.0 }, {2, 2.0} } );

    assert(n.size() == 3);

    assert(n == e);

  }

  {

    const std::multimap<int,double> m ( { {0, 0.0}, { 1, 1.0}, { 1, 2.0}, {2, 2.0} } );

    const std::map<int,double> n(MultimapToMap(m));

    const std::map<int,double> e( { {0, 0.0}, { 1, 1.5 }, {2, 2.0} } );

    assert(n.size() == 3);

    assert(n == e);

  }

  assert(1==2);

}

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(C++) MultimapToMap

Technical facts

Qt project file: ./CppMultimapToMap/CppMultimapToMap.pro

./CppMultimapToMap/main.cpp