Multisets and Multimaps

I was trying to understand where multisets would be used as compared to multimaps and I didnt find any straightforward answer. I found this simple explanation at StackOverflow:

multimap

• With ZIP code as a key, all people which have that ZIP code
• With account ID as key, all open orders of that person/account
• A dictionary, with per keyword various explanations

multiset

is in essence a map with a key and a integer count.

• The inventory of a shop, all products have their key and the amount still available is the value
• accumulated sales data of a shop, every time a product is sold the product id get's added to the multiset thereby increasing the amount sold

As a result I created this example below. This is probably not the best of examples but I didnt want to change it. The main problem below is that multimap's are not strictly speaking required in the example below. I could have used a map. Multimap would be needed if there was no quantity_ in the class and then I can add the products one by one. I could have then used the count method to get the quantity.

Anyway, program as follows:

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//Simple example of multiset

#include <iostream>
#include <string>
#include <set>
#include <map>
#include <algorithm>

using namespace std;

class Product //Keeping this simple
{
public:
Product(string name, int code, int price) :
  name_(name), productCode_(code), price_(price)
  {
    quantity_ = 10; //Lets fix this value for simplicity
    }
bool availableForSale()
{
  if(quantity_ > 0)
  {
    quantity_--;
    return true;
  }
  return false;
}
string name_;
int productCode_;
int price_;
int quantity_;
private:
Product(); //Disabled the default constructor
};

void sellProduct(string name, multimap<string, Product*>& inventory, multiset <int> &soldItems)
{
multimap<string, Product*>::iterator it = inventory.find(name);
if(it != inventory.end())
{
  if ((*it->second).availableForSale())
  {
    soldItems.insert((*it->second).productCode_);
  }
}
else
{
  cout << "Unknown product : " << name << endl;
}
}

void soldItemsList(multimap<string, Product*>& inventory, multiset <int> &soldItems)
{
multimap<string, Product*>::iterator it = inventory.begin();
for(it = inventory.begin(); it != inventory.end(); ++it)
{
  int soldCount = soldItems.count((*it->second).productCode_);
  cout<<"Product = " << (*it->second).name_ << ", Quantity Sold = " << soldCount << endl;
}
}

int checkSales(multimap<string, Product*>& inventory, multiset <int> &soldItems)
{
int totalSales = 0;
multimap<string, Product*>::iterator it;
for(it = inventory.begin(); it != inventory.end(); ++it)
{
  int soldCount = soldItems.count((*it->second).productCode_);
  totalSales += soldCount * (*it->second).price_;
}
return totalSales;
}

int main()
{
//There is no special reason to use multimap instead of a map
//If you wanted to add same product and create quantity multimap is required
  multimap<string, Product*> inventory;
Product* prod1 = new Product("product1", 2334, 10);
Product* prod2 = new Product("product2", 4556, 50);
inventory.insert(pair<string, Product*>("product1",prod1));
inventory.insert(pair<string, Product*>("product2",prod2));

multiset <int> soldItems;

sellProduct("product1", inventory, soldItems);
sellProduct("product2", inventory, soldItems);
sellProduct("apple", inventory, soldItems);
sellProduct("product1", inventory, soldItems);
sellProduct("product1", inventory, soldItems);
sellProduct("product2", inventory, soldItems);

soldItemsList(inventory, soldItems);

cout<<"Total sales = " << checkSales(inventory, soldItems) << endl;

delete prod1;
delete prod2;
return 0;
}

The output as follows:

Instantiating a Multimap inside a class

The following is a very simple example of Instantiating a Multimap. This example was posted as a result of a comment on the actual Multimap example here.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//This program shows use of multi-maps in a class
#include<iostream>
#include<map>
#include <string>

using namespace std;

class mapInstantiator
{
public:
  ~mapInstantiator();
  void createMultiMap(void);
  void insertElements(pair<string, int> element);
  void printer(void);
private:
  multimap<string, int> *phoneNums;
};

void mapInstantiator::createMultiMap(void)
{
  //Instantiate
  phoneNums = new multimap<string, int>;
}

void mapInstantiator::insertElements(pair<string, int> element)
{
  phoneNums->insert(element);
}

void mapInstantiator::printer(void)
{
  cout<<"\n\nMultimap printer method"<<endl;
  cout<<"Map size = "<<phoneNums->size()<<endl;
  multimap<string, int>::iterator it = phoneNums->begin();
  while(it != phoneNums->end())
  {
    cout<<"Key = "<<it->first<<"    Value = "<<it->second<<endl;
    it++;
  }
}

mapInstantiator::~mapInstantiator()
{
  //Dont forget to delete the pointer
  delete phoneNums;
}

int main()
{
  mapInstantiator aClass;
  aClass.createMultiMap();

  //Insert key, value as pairs
  aClass.insertElements(pair<string, int>("Joe",123));
  aClass.insertElements(pair<string, int>("Will",444));
  aClass.insertElements(pair<string, int>("Joe",369));
  aClass.insertElements(pair<string, int>("Joe",812));
  aClass.insertElements(pair<string, int>("Will",4556));
  aClass.insertElements(pair<string, int>("Smith",71));

  aClass.printer();

  return 0;
}

The Output is as follows:

An example of C++ Multimap

The following is a simple example of C++ Multimap class.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//This program shows use of multi-maps
//We input multiple phone numbers for different people
#include<iostream>
#include<map>
#include <string>

using namespace std;

//forward declaration
void printer(multimap<string, int> pN);

int main()
{
  multimap<string, int> phoneNums;

  //Insert key, value as pairs
  phoneNums.insert(pair<string, int>("Joe",123));
  phoneNums.insert(pair<string, int>("Will",444));
  printer(phoneNums);

  //Insert duplicates
  phoneNums.insert(pair<string, int>("Joe",369));
  phoneNums.insert(pair<string, int>("Smith",567));
  phoneNums.insert(pair<string, int>("Joe",888));
  phoneNums.insert(pair<string, int>("Will",999));
  printer(phoneNums);

  //Checking frequency of different keys
  cout<<"\n\nFrequency of different names"<<endl;
  cout<<"Number of Phones for Joe = "<<phoneNums.count("Joe")<<endl;
  cout<<"Number of Phones for Will = "<<phoneNums.count("Will")<<endl;
  cout<<"Number of Phones for Smith = "<<phoneNums.count("Smith")<<endl;
  cout<<"Number of Phones for Zahid = "<<phoneNums.count("Zahid")<<endl;

  //Print all Joe from the list and then erase them
  pair<multimap<string,int>::iterator, multimap<string,int>::iterator> ii;
  multimap<string, int>::iterator it; //Iterator to be used along with ii
  ii = phoneNums.equal_range("Joe"); //We get the first and last entry in ii;
  cout<<"\n\nPrinting all Joe and then erasing them"<<endl;
  for(it = ii.first; it != ii.second; ++it)
  {
    cout<<"Key = "<<it->first<<"    Value = "<<it->second<<endl;
  }
  phoneNums.erase(ii.first, ii.second);
  printer(phoneNums);

  return 0;
}

//This method prints the vector
void printer(multimap<string, int> pN)
{
  cout<<"\n\nMultimap printer method"<<endl;
  cout<<"Map size = "<<pN.size()<<endl;
  multimap<string, int>::iterator it = pN.begin();
  while(it != pN.end())
  {
    cout<<"Key = "<<it->first<<"    Value = "<<it->second<<endl;
    it++;
  }
}

The output is as follows: