Type Parameters

  • TKey
    The type of keys in the dictionary.

  • TValue
    The type of the values in the dictionary.
The Dictionary<TKey,TValue> is a member of "System.Collections.Generic" namespace it's a generic collection which is generally used to store key/value pairs data. Each and every key must be unique in the dictionary.
Example
Dictionary Initialization.
Dictionary<string,string> dictionary= newDictionary<string,string>();
Example 1
Creates a dictionary and Retrieve Items of a Dictionary in C#.
The following code snippet creates a dictionary where the key type is int and value type is a string.
  1. IDictionary<int, string> NumberDictionary = new Dictionary<int, string>();
The following code snippet adds items to the dictionary.
  1. NumberDictionary.Add(1, "One");
  2. NumberDictionary.Add(2, "Two");
  3. NumberDictionary.Add(3, "Three");
The Dictionary is a collection. We can use the foreach loop to go through all the items and read them using they Key and Value properties.
  1. Console.WriteLine("--Number Dictionaty--");
  3. foreach (KeyValuePair<int , string> item in NumberDictionary)
  4. {
  5. Console.WriteLine($"Key: {item.Key}, Value: {item.Value}");
  6. }
Output
C# Dictionary <TKey, TValue />
Example 2
Creates a dictionary and Retrieve Items of a Dictionary in C#.
The following code snippet creates a dictionary where the key type is char and value type is List<string>.
  1. IDictionary<char,List<string>> ContryNameDictionary = new Dictionary<char, List<string>>();
The following code snippet creates a list where collection of country name alphabet wise.
  1. List<string> ContryNameStartWith_A = new List<string> { "Afghanistan", "Albania", "Algeria", "Andorra" };
  2. List<string> ContryNameStartWith_B = new List<string> { "Bahamas", "Bahrain", "Bangladesh", "Barbados" };
  3. List<string> ContryNameStartWith_C = new List<string> { "Cambodia", "Cameroon", "Canada", "Cape Verde" };
The following code snippet adds items to the dictionary.
  1. ContryNameDictionary.Add('A', ContryNameStartWith_A);
  2. ContryNameDictionary.Add('B', ContryNameStartWith_B);
  3. ContryNameDictionary.Add('C', ContryNameStartWith_C);
The Dictionary is a collection. We can use the foreach loop to go through all the items and read them using they Key and Value properties.
  1. Console.WriteLine("--Alphabet Wise Country Name Dictionaty--");
  3. foreach (KeyValuePair<char, List<string>> item in ContryNameDictionary)
  4. {
  5. Console.WriteLine($"Alphabet: {item.Key}, --> Contry Name: {string.Join(", ",ContryNameDictionary[item.Key])}");
  6. }
Output
C# Dictionary <TKey, TValue />
Example 3
The following code snippet creates a user-defined class, StudentInfo.
  1. public class StudentInfo
  2. {
  3. public string Name { get; set; }
  4. public string Gender { get; set; }
  5. public string Standard { get; set; }
  6. public int Total { get; set; }
  7. }
The following code snippet creates a dictionary where the key type is int(Student Roll Number) and value type is user-defined class StudentInfo.
  1. IDictionary<int, StudentInfo> StudentInfoDictionary = new Dictionary<int, StudentInfo>();
The following code snippet creates a list where collection of student information.
  1. StudentInfo student1 = new StudentInfo() { Name = "Emma", Gender = "Female", Standard = "10", Total =506};
  2. StudentInfo student2 = new StudentInfo() { Name = "Liam", Gender = "Male", Standard = "12", Total = 600 };
  3. StudentInfo student3 = new StudentInfo() { Name = "Noah", Gender = "Male", Standard = "09", Total = 550 };
  4. StudentInfo student4 = new StudentInfo() { Name = "Olivia", Gender = "Female", Standard = "08", Total = 685 };
  5. StudentInfo student5 = new StudentInfo() { Name = "Ava", Gender = "Female", Standard = "11", Total = 605 };
  6. StudentInfo student6 = new StudentInfo() { Name = "Oliver", Gender = "Male", Standard = "10", Total = 700 };
The following code snippet adds items to the dictionary.
  1. StudentInfoDictionary.Add(1, student1);
  2. StudentInfoDictionary.Add(2, student2);
  3. StudentInfoDictionary.Add(3, student3);
  4. StudentInfoDictionary.Add(4, student4);
  5. StudentInfoDictionary.Add(5, student5);
  6. StudentInfoDictionary.Add(6, student6);
The Dictionary is a collection. We can use the foreach loop to go through all the items and read them using they Key and Value properties.
  1. Console.WriteLine("--Student Information Dictionaty--");
  3. foreach (KeyValuePair<int, StudentInfo> item in StudentInfoDictionary)
  4. {
  5. Console.WriteLine($"Roll No: {item.Key}");
  6. Console.Write($"Name: {StudentInfoDictionary[item.Key].Name}");
  7. Console.Write($", Gender: {StudentInfoDictionary[item.Key].Gender}");
  8. Console.Write($", Standard: {StudentInfoDictionary[item.Key].Standard}");
  9. Console.WriteLine($", Total: {StudentInfoDictionary[item.Key].Total}");
  10. Console.WriteLine("-------------------------------------------------------");
  11. }
Output
C# Dictionary <TKey, TValue />
Example - ContainsKey() & Contains()
Determines whether the Dictionary<TKey,TValue> contains the specified key and contains.
  1. Console.WriteLine($"Example: ContainsKey() & Contains()");
  2. Console.WriteLine($"StudentInfoDictionary have key 5 = {StudentInfoDictionary.ContainsKey(5)}");
  3. Console.WriteLine($"StudentInfoDictionary have key 7 = {StudentInfoDictionary.ContainsKey(7)}");
  4. Console.WriteLine($"StudentInfoDictionary have Contains key=1 and value=student1 result = {StudentInfoDictionary.Contains(new KeyValuePair<int, StudentInfo>(1, student1))}");
  5. Console.WriteLine($"StudentInfoDictionary have Contains key=4 and value=student2 result = {StudentInfoDictionary.Contains(new KeyValuePair<int, StudentInfo>(4, student2))}");
Output
C# Dictionary <TKey, TValue />
Example - TryGetValue()
Gets the value associated with the specified key.
  1. StudentInfo result;
  3. if (StudentInfoDictionary.TryGetValue(4, out result))
  4. {
  5. Console.WriteLine($"Example: TryGetValue()");
  6. Console.Write($"Name: {result.Name}");
  7. Console.Write($", Gender: {result.Gender}");
  8. Console.Write($", Standard: {result.Standard}");
  9. Console.WriteLine($", Total: {result.Total}");
  10. }
  11. else
  12. {
  13. Console.WriteLine("Could not find the specified key.");
  14. }
Output
C# Dictionary <TKey, TValue />
Example - Remove elements from Dictionary
Removes the value with the specified key from the Dictionary<TKey,TValue>.
  1. Console.WriteLine("--Before Remove Key 2--");
  2. foreach (KeyValuePair<int, StudentInfo> item in StudentInfoDictionary)
  3. {
  4. Console.WriteLine($"Roll No: {item.Key}, Name: {StudentInfoDictionary[item.Key].Name}");
  5. }
  7. StudentInfoDictionary.Remove(2);
  9. Console.WriteLine("-- StudentInfoDictionary.Remove(2);--");
  10. Console.WriteLine("--After Remove Key 2 and Befoer Remove Key=3 and Value=Student3 --");
  12. foreach (KeyValuePair<int, StudentInfo> item in StudentInfoDictionary)
  13. {
  14. Console.WriteLine($"Roll No: {item.Key}, Name: {StudentInfoDictionary[item.Key].Name}");
  15. }
  17. StudentInfoDictionary.Remove(new KeyValuePair<int, StudentInfo>(3, student3));
  18. Console.WriteLine("StudentInfoDictionary.Remove(new KeyValuePair<int, StudentInfo>(3, student3));");
  20. foreach (KeyValuePair<int, StudentInfo> item in StudentInfoDictionary)
  21. {
  22. Console.WriteLine($"Roll No: {item.Key}, Name: {StudentInfoDictionary[item.Key].Name}");
  23. }
Output
Want to learn more? Here is a detailed tutorial: Dictionary in C#