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>.
  1. // Creating a dictionary
  2. // using Dictionary<TKey,TValue> class
  3. Dictionary<int, string> empList =
  4. new Dictionary<int, string>();
  6. // Add() method - For Adding key/value pairs in the Dictionary
  7. // Employee Code and Name
  8. empList.Add(1, "X");
  9. empList.Add(2, "Y");
  10. empList.Add(3, "Z");
  12. foreach (KeyValuePair<int, string> emp in empList)
  13. {
  14. Console.WriteLine($"Employee Code - {emp.Key}, Employee Name - {emp.Value}");
  15. }
  17. // Creating another dictionary
  18. // using Dictionary<TKey,TValue> class
  19. // adding key/value pairs without
  20. // using Add method - Department/EmpName
  21. Dictionary<string, string> empList2 =
  22. new Dictionary<string, string>(){
  23. {"IT", "Rahul"},
  24. {"Dev", "Raj"},
  25. {"HR", "Ayesha"} };
  27. foreach (KeyValuePair<string, string> emp in empList2)
  28. {
  29. Console.WriteLine($" Department - {emp.Key}, Employee Name - {emp.Value}");
  30. }
  32. #region Check Element/Value is Present
  34. // Using ContainsKey() method to check
  35. // the specified key is present or not
  36. if (empList.ContainsKey(3) == true)
  37. {
  38. Console.WriteLine("Key is found...!!");
  39. }
  41. else
  42. {
  43. Console.WriteLine("Key is not found...!!");
  44. }
  46. // Using ContainsValue() method to check
  47. // the specified value is present or not
  48. if (empList.ContainsValue("Z") == true)
  49. {
  50. Console.WriteLine("Value is found...!!");
  51. }
  53. else
  54. {
  55. Console.WriteLine("Value is not found...!!");
  56. }
  58. #endregion
  60. #region Remove Elements
  62. // Using Remove() method
  63. empList.Remove(2);
  65. // After Remove() method
  66. foreach (KeyValuePair<int, string> emp in empList)
  67. {
  68. Console.WriteLine($"Employee Code - {emp.Key}, Employee Name - {emp.Value}");
  69. }
  70. Console.WriteLine();
  73. // Using Clear() method
  74. empList.Clear();
  76. Console.WriteLine($"Total key/value pairs present in empList:{empList.Count}");
  78. #endregion