Associative Arrays  

  • Associative array:

    • is not stored as a traditional array

    • is called an "array" because usage resembles that of an array (i.e.: A[i])

  • What is an Associative array:

    • maps keys to their corresponding values

      Example: 

        Name (key)      Phone (value)
  ---------       --------
  john            123-4567       (A["john"] = "123-4567")
  mary            333-3333       (A["mary"] = "333-3333")

  Associative array in C++: map  

  • Associative array in C++ is called: map

  • Defining a map: 

      #include <map>

  map<string, string> map1;
  // Defines an empty map of string -> string

  map<string, string> map2 = { {"john", "123-4567"},
                               {"mary", "333-3333"},
                               {"jack", "345-6666"},
                               {"amos", "222-8888"},
                               {"jane", "444-5555"} }
  
  // Defines a map of int with initial mapping:
  //      "john" -> "123-4567"
  //      "mary" -> "333-3333"}
  //      "jack" -> "345-6666"}
  //      "amos" -> "222-8888"}
  //      "jane" -> "444-5555"}

  Associative array in C++: map  

  • Accessing values stored in a map: 

      map2["john"]       // Access the value associated with "john"
  map2["mary"]       // Access the value associated with "mary"

  • Accessing a map using a for-loop: 

      for (auto  data: map2 )
     cout << data.first << "  " << data.second << endl;
 
  // first  is the key
  // second is the value corresponding to the key
  // data is a help variable

  Associative array in C++: map  

  • Inserting values into a map: 

      map2["new"] = "999-9999";    // Inserts new -> 999-9999 to map

  • Deleting values from a map: 

      map2.erase("new");    // Removes the key new and its value from map

  • Updating values stored a map: 

      map2["amos"] = "000-0000;  // Updates the value in map2["amos"]

Demo program: map.cc

  Associative array in Python: dict (dictionary)  

  • Associative array in Python is called: dict (= dictionary)

  • Defining a dictionary: 

      dict1 = []
  # Defines an empty dict

  dict2 = { "john" : "123-4567",
            "mary" : "333-3333",
            "jack" : "345-6666",
            "amos" : "222-8888",
            "jane" : "444-5555"  }

  # Defines a map of int with initial mapping:
  #      "john" -> "123-4567"
  #      "mary" -> "333-3333"}
  #      "jack" -> "345-6666"}
  #      "amos" -> "222-8888"}
  #      "jane" -> "444-5555"}

  Associative array in Python: dict (dictionary)  

  • Accessing values stored in a map: 

      map2["john"]       // Access the value associated with "john"
  map2["mary"]       // Access the value associated with "mary"

  • Accessing a map using a for-loop: 

     for k in dict2:
    print( k, dict2[k] )

 # I used "k" to denote "key"
 # dict[k] is the value asscoiate with the key k

  Associative array in Python: dict (dictionary)  

  • Inserting values into a dict: 

     dict2["new"] = "999-9999";    # Inserts new -> 999-9999 to dict2

  • Deleting values from a dict: 

      del dict2["new"];    // Removes the key new and its value from dict2

  • Updating values stored a dict: 

      dict2["amos"] = "000-0000;  // Updates the value in dict2["amos"]

Demo program: dict.py