C++/Map Multimap/transform

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Transform vector of user-defined objects to a multi-map

<source lang="cpp">

  1. include <algorithm>
  2. include <functional>
  3. include <iomanip>
  4. include <iostream>
  5. include <map>
  6. include <string>
  7. include <utility>
  8. include <vector>

using namespace std; class PC {

  public:
  enum PC_type { Dell, HP, IBM, Compaq };
  PC( PC_type appliance = Dell, int model = 220,
     int serial = 0 );
  bool operator<( const PC& rhs ) const;
  PC_type appliance() const;
  int model() const;
  string name() const;
  void print() const;
  int serial() const;
  private:
  PC_type appliance_;
  int model_;
  int serial_;

}; inline PC::PC( PC::PC_type appliance, int model,int serial )

  : appliance_( appliance ), model_( model ), serial_( serial )

{} // empty inline bool PC::operator<( const PC& rhs ) const { return appliance() < rhs.appliance() ||

  ( appliance() == rhs.appliance() && model() < rhs.model() );

} inline PC::PC_type PC::appliance() const { return appliance_; } inline int PC::model() const { return model_; } string PC::name() const {

  string what;
  switch( appliance() )
  {
     case Dell:    what = "Dell";              break;
     case HP:      what = "HP";                break;
     case IBM:     what = "IBM";               break;
     case Compaq:  what = "Compaq";            break;
     default:      what = "Unknown appliance"; break;
  }
  return what;

} inline void PC::print() const {

  char oldfill = cout.fill();
  cout << name() << " - Model "
       << model() << ", Serial number " 
       << serial() << endl;

} inline int PC::serial() const { return serial_; } bool greater_model( const pair<PC::PC_type,PC> p,int min_model ); int main( ) {

  const PC::PC_type kind[] = { PC::IBM,PC::IBM, PC::Dell, PC::HP,PC::HP, PC::HP };
  const int num_appliances = 3;
  vector<PC> v;
  for( int i = 0; i < num_appliances; ++i )
     v.push_back( PC( kind[i], i, i ) );
  map<int,PC> sold;
  transform( kind, kind+num_appliances, v.begin(),inserter( sold, sold.end() ),make_pair<int,PC> );
  map<int,PC>::const_iterator sold_end = sold.end();
  // work with a multimap. key is appliance type, value is PC
  typedef multimap<PC::PC_type,PC> PC_multimap_type;
  PC_multimap_type stock;
  const PC desired( PC::HP );
  
  // load the appliances into the multimap
  transform( kind, kind+num_appliances, v.begin(),inserter( stock, stock.end() ), make_pair<PC::PC_type,PC> );
  PC_multimap_type::const_iterator stock_end = stock.end();
  // search for first occurrence of key
  PC_multimap_type::const_iterator spot = stock.find( desired.appliance() );
  if( spot != stock_end )
     spot->second.print();
  else
     cout << "Don"t have a " << desired.name() << " in stock\n";

} inline bool greater_model( const pair<PC::PC_type,PC> p,int min_model ) { return p.second.model() >= min_model; }



 </source>


use transform() to create map from two arrays

<source lang="cpp">

  1. include <algorithm>
  2. include <iostream>
  3. include <map>
  4. include <utility>

using namespace std; int main( ) {

  const char* word[] = { "A", "B", "C", "D","E" };
  const char* clue[] = { "a", "b","c", "d","e" };
  map<string,string> dictionary1;
  transform( word, word+sizeof(word)/sizeof(word[0]), clue,inserter( dictionary1, dictionary1.end() ),make_pair<string,string> );
  cout << "There are " << dictionary1.size() << " words in the dictionary\n\n";

}


 </source>


Use transform to fill a map from a vector of user-defined object

<source lang="cpp">

  1. include <algorithm>
  2. include <functional>
  3. include <iomanip>
  4. include <iostream>
  5. include <map>
  6. include <string>
  7. include <utility>
  8. include <vector>

using namespace std; class PC{

  public:
  enum PC_type { Dell, HP, IBM, Compaq };
  PC( PC_type appliance = Dell, int model = 220,int serial = 0 );
  bool operator<( const PC& rhs ) const;
  PC_type appliance() const;
  int model() const;
  string name() const;
  void print() const;
  int serial() const;
  private:
  PC_type appliance_;
  int model_;
  int serial_;

}; inline PC::PC( PC::PC_type appliance, int model,int serial )

  : appliance_( appliance ), model_( model ), serial_( serial )

{} inline bool PC::operator<( const PC& rhs ) const { return appliance() < rhs.appliance() ||

  ( appliance() == rhs.appliance() && model() < rhs.model() );

} inline PC::PC_type PC::appliance() const { return appliance_; } inline int PC::model() const { return model_; } string PC::name() const {

  string what;
  switch( appliance() )
  {
     case Dell:         what = "Dell";              break;
     case HP:           what = "HP";                break;
     case IBM:          what = "IBM";               break;
     case Compaq:       what = "Compaq";            break;
     default:           what = "Unknown appliance"; break;
  }
  return what;

} inline void PC::print() const {

  char oldfill = cout.fill();
  cout << name() << " - Model "
       << model() << ", Serial number " 
       << serial() << endl;

} inline int PC::serial() const { return serial_; } bool greater_model( const pair<PC::PC_type,PC> p,int min_model ); int main( ) {

  const PC::PC_type kind[] = { PC::IBM,PC::Dell, PC::HP};
  int num_appliances = 3, serial=0;
  vector<PC> v;
  for( int i = 0; i < 3; ++i )
     v.push_back( PC( kind[i], i, i ) );
  map<int,PC> sold;
   
  transform( kind, kind+num_appliances, v.begin(),inserter( sold, sold.end() ),make_pair<int,PC> );
  map<int,PC>::const_iterator sold_end = sold.end();
  map<int,PC>::const_iterator site;
  for( site = sold.begin(); site != sold_end; ++site )
     site->second.print();

}



 </source>