.NET Collections - Generic Collection - Dictionary<Tkey, TValue>

In this blog, you will learn how to create a Dictionary and perform Add, Remove, Sort, Search, and other operations on a List.

Dictionary is a generic collection used to store key/value pairs. Dictionary's work is very similar to the non-generic hashtable. Dictionary is defined under System.Collection.Generic namespace. The dictionary's size increases as needed. The Dictionary class uses interface, IReadOnlyCollection < KeyValuePair < TKey, TValue > Interface, IReadOnlyDictionary < TKey, TValue > Interface, and IDictionary Interface.

 

Key Points about Dictionary

1. Key in a dictionary cannot be null; however, a value can be.
2. Key in the dictionary must be unique.
3. Dictionary is strongly typed, this means the dictionary accepts key/value of only the same types are defined.

Please refer to the below code which shows all the operations we can perform on Dictionary<TKey,TValue>.

// Creating a dictionary
// using Dictionary<TKey,TValue> class
Dictionary<int, string> empList =
               new Dictionary<int, string>();

// Add() method - For Adding key/value pairs in the Dictionary
// Employee Code and Name
empList.Add(1, "X");
empList.Add(2, "Y");
empList.Add(3, "Z");

foreach (KeyValuePair<int, string> emp in empList)
{
    Console.WriteLine($"Employee Code - {emp.Key}, Employee Name - {emp.Value}");
}

// Creating another dictionary
// using Dictionary<TKey,TValue> class
// adding key/value pairs without
// using Add method  - Department/EmpName
Dictionary<string, string> empList2 =
        new Dictionary<string, string>(){
                      {"IT", "Rahul"},
                      {"Dev", "Raj"},
                    {"HR", "Ayesha"} };

foreach (KeyValuePair<string, string> emp in empList2)
{
    Console.WriteLine($" Department - {emp.Key}, Employee Name - {emp.Value}");
}

#region Check Element/Value is Present

// Using ContainsKey() method to check
// the specified key is present or not
if (empList.ContainsKey(3) == true)
{
    Console.WriteLine("Key is found...!!");
}

else
{
    Console.WriteLine("Key is not found...!!");
}

// Using ContainsValue() method to check
// the specified value is present or not
if (empList.ContainsValue("Z") == true)
{
    Console.WriteLine("Value is found...!!");
}

else
{
    Console.WriteLine("Value is not found...!!");
}

#endregion

#region Remove Elements

// Using Remove() method
empList.Remove(2);

// After Remove() method
foreach (KeyValuePair<int, string> emp in empList)
{
    Console.WriteLine($"Employee Code - {emp.Key}, Employee Name - {emp.Value}");
}
Console.WriteLine();


// Using Clear() method
empList.Clear();

Console.WriteLine($"Total key/value pairs present in empList:{empList.Count}");

#endregion