Dictionary Data Structure

Dictionary is one of the important Data Structures that is usually used to store data in the key-value format. Each element presents in a dictionary data structure compulsorily have a key and some value is associated with that particular key. In other words, we can also say that Dictionary data structure is used to store the data in key-value pairs. Other names for the Dictionary data structure are associative array, map, symbol table but broadly it is referred to as Dictionary.

A dictionary or associative array is a general-purpose data structure that is used for the storage of a group of objects.

Many popular languages add Dictionary or associative array as a primitive data type in their languages while other languages which don't consider Dictionary or associative array as a primitive data type have included Dictionary or associative array in their software libraries. A direct form of hardware-level support for the Dictionary or associative array is Content-addressable memory.

In Dictionary or associative array, the relation or association between the key and the value is known as the mapping. We can say that each value in the dictionary is mapped to a particular key present in the dictionary or vice-versa.

The various operations that are performed on a Dictionary or associative array are:

Add or Insert: In the Add or Insert operation, a new pair of keys and values is added in the Dictionary or associative array object.
Replace or reassign: In the Replace or reassign operation, the already existing value that is associated with a key is changed or modified. In other words, a new value is mapped to an already existing key.
Delete or remove: In the Delete or remove operation, the already present element is unmapped from the Dictionary or associative array object.
Find or Lookup: In the Find or Lookup operation, the value associated with a key is searched by passing the key as a search argument.

Now, let us see the usage of the dictionary data structure in different programming languages.

Python:

A sample python code to perform all the basic four operations like create, update, delete and update.

Code:

# creating a dictionary object named players having key as jersey number and value as the name of the player 
players=dict()


# function to add or insert data into the dictionary object named players
def take_input():

	print('Enter the jersey number to be entered')
	key = int(input())
	print('Enter the player name to be entered')
	value = input()

	players[key]=value


# function to udpate the values of the elements of the 
 object named players
def update_values():

	print('Enter the key whose value you want to update')
	key=int(input())
	print('Enter the new value that you want to assign to the key entered')
	new_value=input()

	players[key]=new_value


# function to delete the elements of the dictionary object named players
def delete_elements():

	print('Enter the key that you want to delete or remove from the dictionary object')
	key=int(input())

	players.pop(key)




# function to print all the elements of the dictionary object named players
def print_dictionary():
	print(players)





# calling the input fucntion
take_input()
# calling the printing fucntion
print_dictionary()
take_input()
take_input()
take_input()
print_dictionary()
# calling the updation fucntion
print('The dictionary after updating the values is:')
update_values()
print_dictionary()
# calling the deletion fucntion
print('The dictionary after deleting the values is:')
delete_elements()
print_dictionary()

Output:

Enter the jersey number to be entered
45
Enter the player name to be entered
Rohit Sharma
{45: 'Rohit Sharma'}
Enter the jersey number to be entered
18
Enter the player name to be entered
Virat Kholi
Enter the jersey number to be entered
7
Enter the player name to be entered
Mahendra Singh Dhoni
Enter the jersey number to be entered
42
Enter the player name to be entered
Shikar Dhawan
{45: 'Rohit Sharma', 18: 'Virat Kholi', 7: 'Mahendra Singh Dhoni', 42: 'Shikar Dhawan'}

Enter the key whose value you want to update
42
Enter the new value that you want to assign to the key entered
Shikhar Dhawan
The dictionary after updating the values is:
{45: 'Rohit Sharma', 18: 'Virat Kholi', 7: 'Mahendra Singh Dhoni', 42: 'Shikhar Dhawan'}

Enter the key that you want to delete or remove from the dictionary object
18
The dictionary after deleting the values is:
{45: 'Rohit Sharma', 7: 'Mahendra Singh Dhoni', 42: 'Shikhar Dhawan'}

In this code, we have created a dictionary object named players having key as integer and value as

Strings. We have also created functions to implement all the basic four functionalities of the dictionary that are create, delete, update, etc.

As we can see in the output of the above code, we have 4 elements as input to our dictionary object created and then update one value in the dictionary and then we deleted one value in the dictionary and in the last we have printed the final dictionary object.

Java

A sample java code to perform all the basic operations like create, delete and update.

Code:

// java code to implement all the basic fucntionalites[add, remove. print, search] of the Dictionary Data Structure

// importing all the required classes for creating a dictionary in Java.
import java.util.Scanner;
import java.util.Hashtable;
import java.util.Dictionary;
import java.util.Enumeration;

// A class named DictionaryJava is created that will consist of four functions to implement all the utilities of the Dictionary
class DictionaryJava{

	// a Dictionary object by the name dictObject is created with the help of Hashtable class
	static Dictionary dictObject =  new Hashtable();
	
	// a Scanner object is created to take input from the user
	static Scanner sc = new Scanner(System.in);

	// a function named add_element is created to add the elements in the Dictionary object named dictObject
	public static void add_element(){

		System.out.println("Enter the key for the Dictionary Object");
		String key = sc.nextLine();
		System.out.println("Enter the value for the Dictionary Object");
		String value = sc.nextLine();

		dictObject.put(key,value);

	}

	// a function named print_dictionary is created to print the elements in the Dictionary object named dictObject
	public static void print_dictionary(){

		System.out.println( dictObject.toString() );

	}

	// a function named remove_element is created to delete or remove the elements from the Dictionary object named dictObject
	public static void remove_element(){

		System.out.println("Enter the key of the element that you want to remove or delete ");
		String key = sc.nextLine();

		dictObject.remove(key);
	}

	// a function named search_element is created to find or search the elements in the Dictionary object named dictObject
	public static void search_element(){

		System.out.println("Enter the key of the element that you want to search or find ");
		String key = sc.nextLine();

		System.out.println("Value of the key " + key + " is " + dictObject.get(key));

	}

}

// a Main class is created to call the utility functionalities from the DictionaryJava class
public class Main{

	public static void main(String ... nk){
		
		// an object of DictionaryJava is created by the name object
		DictionaryJava object = new DictionaryJava();

		// add_element fucntion of the DictionaryJava is called to add data in the Dictionary object  
		object.add_element();
		object.add_element();

		// print_dictionary fucntion of the DictionaryJava is called to print the data of the Dictionary object
		object.print_dictionary();

		// remove_element fucntion of the DictionaryJava is called to remove or delete the data of the Dictionary object
		object.remove_element();
		System.out.println("Dictionary after removing the element(s)");
		object.print_dictionary();

		// search_element fucntion of the DictionaryJava is called to search or find the data of the Dictionary object
		object.search_element();

	}
}

Output:

Enter the key for the Dictionary Object
name
Enter the value for the Dictionary Object
Nirnay Khajuria
Enter the key for the Dictionary Object
age
Enter the value for the Dictionary Object
23
{age=23, name=Nirnay Khajuria}


Enter the key of the element that you want to remove or delete 
age
Dictionary after removing the element(s)
{name=Nirnay Khajuria}


Enter the key of the element that you want to search or find 
name
The value of the key name is Nirnay Khajuria

In this code, we have created a dictionary object named dictObject having key as string and value as

Strings. We have also created functions to implement all the basic four functionalities of the dictionary that are the create, delete, update, search, etc.

As we can see in the output of the above code, we have two elements as input to our dictionary object created and then update one value in the dictionary and then we searched one value in the dictionary and in the last we have printed the final dictionary object that we have created.

CPP:

Now let us write a C++ code that will give us an idea about how to use Dictionary or associative array and their basic functionalities in C++.

Code:

// c++ code to implement all the basic fucntionalites[add, remove. print, search] of the Dictionary Data Structure


// iostream library is included for basic input output operations  
#include <iostream> 
// map library is included to use map in our c++ code 
#include <map>
// string header is also included in the code to make use of the string objects in the c++ code
#include <string>

using namespace std;


// a map object is created that will stores strings indexed by strings ( that means both the key and the value will be of the string type.)
// NOTE: In C++ we need to explicitly specify the data type of the key and values to be stored in the map or dictionary object
std::map<std::string, std::string> capitals;



// a fucntion named insert_elements is created to add elements into the map or dictionary object named capitals
void insert_elements(){

    std::string key;
    std::string value;

    std::cout<<"\nEnter the name of the country : ";
    std::cin>>key;
    std::cout<<"Enter the capital of "<<key<<" : ";
    std::cin>>value;

    
    // value is mapped to the key and inserted successfully to the map or dictionary object named capitals
    capitals[key]=value;

}



// a fucntion named print_elements is created to all the elements present in the capitals dictionary object  
void print_elements(){


    // each element of the capitals object of the dictionary is iterated and printed
    for ( auto item : capitals ) {
        
        std::cout <<"Name of the country "<< item.first << ": Name of the capital ";
        std::cout << item.second << std::endl;
    }


}

// a fucntion named delete_elements is created to delete element or elements from the dictionary object named capitals
void delete_elements(){

    std :: string key_to_be_deleted;

    std :: cout << "\nEnter the name of the country that you want to delete : ";
    std :: cin >> key_to_be_deleted;

    capitals.erase(key_to_be_deleted);

}

// a function named search_elements is created to perform search or find operation on the capitals dictionary object
void search_elements(){

    std :: string key_to_be_searched;

    std :: cout << "\nEnter the name of the country that you want to search : ";
    std :: cin >> key_to_be_searched;

    std :: cout << "Capital of "<< key_to_be_searched << " is " << capitals[key_to_be_searched]<< "\n"; 

}


// a fucntion named update_elements is created to update_elements is created to update or modify the already present elements in the dictionary object
void update_elements(){

    std :: string key_to_be_updated;
    std :: string new_key;    

    std :: cout << "\nEnter the name of the country whose capital you want to update : ";
    std :: cin >> key_to_be_updated;
    std :: cout << "Enter the name of new capital : ";
    std :: cin >> new_key;

    capitals[key_to_be_updated]=new_key;

}

// main function is written to handle the execution of the code.
int main()
{
    
    int choice;


    // a menu-driven program is written to call the various functions that does various operations on the dictionary object named capitals

    while(1){


        std::cout<<"\n1. To insert data into the Dictionary."<<std::endl;
        std::cout<<"2. To print data from the Dictionary."<<std::endl;
        std::cout<<"3. To delete data from the Dictionary."<<std::endl;
        std::cout<<"4. To search data from the Dictionary."<<std::endl;
        std::cout<<"5. To update data from the Dictionary."<<std::endl;
        std::cout<<"0. To exit the code."<<std::endl;
        std::cout<<"Enter your choice:";

        std::cin>>choice;


        switch(choice){

            case 0 : 

                // to exit the code.
                exit(0);

            case 1 :

                // to insert elements in the dictionary object
                insert_elements();
                break;

            case 2 :


                // to print elements in the dictionary object
                std::cout<<std::endl;
                std::cout<<"Contents of the Dictionary are : \n";
                print_elements();
                break;

            case 3 :


                // to delete elements in the dictionary object
                std::cout<<std::endl;
                delete_elements();
                std::cout<<"Element deleted sucessfully.\n";
                break;

            case 4 :


                // to search elements in the dictionary object
                std::cout<<std::endl;
                std::cout<<"Result of the search in the dictionary is  : ";
                search_elements();
                break;

            case 5 :


                // to update elements in the dictionary object
                std::cout<<std::endl;
                update_elements();
                std::cout<<"Contents of the Dictionary updated sucessfully.\n";
                break;

            default :

                std::cout<<"Please Enter valid input.";

        }

    }

    return 0;
}
//end of the main function

Output:

1. To insert data into the Dictionary.
2. To print data from the Dictionary.
3. To delete data from the Dictionary.
4. To search data from the Dictionary.
5. To update data from the Dictionary.
0. To exit the code.
Enter your choice:1

Enter the name of the country : India
Enter the capital of India : Delhi

1. To insert data into the Dictionary.
2. To print data from the Dictionary.
3. To delete data from the Dictionary.
4. To search data from the Dictionary.
5. To update data from the Dictionary.
0. To exit the code.
Enter your choice:1

Enter the name of the country : Dominica
Enter the capital of Dominica : Roseau

1. To insert data into the Dictionary.
2. To print data from the Dictionary.
3. To delete data from the Dictionary.
4. To search data from the Dictionary.
5. To update data from the Dictionary.
0. To exit the code.
Enter your choice:1

Enter the name of the country : Haiti
Enter the capital of Haiti : Port-au-prince

1. To insert data into the Dictionary.
2. To print data from the Dictionary.
3. To delete data from the Dictionary.
4. To search data from the Dictionary.
5. To update data from the Dictionary.
0. To exit the code.
Enter your choice:1

Enter the name of the country : USA
Enter the capital of USA : Washington

1. To insert data into the Dictionary.
2. To print data from the Dictionary.
3. To delete data from the Dictionary.
4. To search data from the Dictionary.
5. To update data from the Dictionary.
0. To exit the code.
Enter your choice:2

Contents of the Dictionary are : 
Name of the country Dominica: Name of the capital Roseau
Name of the country Haiti: Name of the capital Port-au-prince
Name of the country India: Name of the capital Delhi
Name of the country USA: Name of the capital Washington

1. To insert data into the Dictionary.
2. To print data from the Dictionary.
3. To delete data from the Dictionary.
4. To search data from the Dictionary.
5. To update data from the Dictionary.
0. To exit the code.
Enter your choice:3


Enter the name of the country that you want to delete : Haiti
Element deleted successfully.

1. To insert data into the Dictionary.
2. To print data from the Dictionary.
3. To delete data from the Dictionary.
4. To search data from the Dictionary.
5. To update data from the Dictionary.
0. To exit the code.
Enter your choice:2

Contents of the Dictionary are : 
Name of the country Dominica: Name of the capital Roseau
Name of the country India: Name of the capital Delhi
Name of the country USA: Name of the capital Washington

1. To insert data into the Dictionary.
2. To print data from the Dictionary.
3. To delete data from the Dictionary.
4. To search data from the Dictionary.
5. To update data from the Dictionary.
0. To exit the code.
Enter your choice:4

Result of the search in the dictionary is  : 
Enter the name of the country that you want to search : USA
Capital of USA is Washington

1. To insert data into the Dictionary.
2. To print data from the Dictionary.
3. To delete data from the Dictionary.
4. To search data from the Dictionary.
5. To update data from the Dictionary.
0. To exit the code.
Enter your choice:5


Enter the name of the country whose capital you want to update : India
Enter the name of new capital : New-Delhi       
Contents of the Dictionary updated sucessfully.

1. To insert data into the Dictionary.
2. To print data from the Dictionary.
3. To delete data from the Dictionary.
4. To search data from the Dictionary.
5. To update data from the Dictionary.
0. To exit the code.
Enter your choice:2

Contents of the Dictionary are : 
Name of the country Dominica: Name of the capital Roseau
Name of the country India: Name of the capital New-Delhi
Name of the country USA: Name of the capital Washington

1. To insert data into the Dictionary.
2. To print data from the Dictionary.
3. To delete data from the Dictionary.
4. To search data from the Dictionary.
5. To update data from the Dictionary.
0. To exit the code.
Enter your choice:0

As we can see in the above code, we have successfully implemented all the basic operations that are search, update, insert, delete and print an object of dictionary named capitals that we have created to store the name of the countries and their respective capitals.

Different functions are created for all of the operations that are mentioned above. First, we created a dictionary and added elements to this created object. Once the insertion of the data is completed in the object, we displayed the added data. After displaying, we deleted already existing data from the dictionary object. After deletion, a searching and updation operations are performed on the dictionary object storing the name of the countries and their respective capitals that are searched and updated various elements from the dictionary object respectively.

So, this article explains the Dictionary Data Structure and what are the basic functions or operations that we can perform on a Dictionary Data Structure object. We also understood the usage of the Dictionary Data Structure in various programming languages like Java, Python, and C++ along with their functionalities that are required to perform the basic operations on this Data Structure. Other than these examples, there are various scenarios where we can use the Dictionary Data Structure. The most ideal scenario for using the Dictionary Data Structure where we need to store our data in key-value pairs.

Next TopicStructured Data and Unstructured Data

← prev next →