Dictionary Methods in C#

Dictionary is a collection of keys and values in C#. Dictionary<TKey, TValue> is included in the System.Collections.Generic namespace and provides methods to add, remove, and search for key-value pairs efficiently.

Common Dictionary Methods

Using Add() and Count

The Add()Count property returns the total number of elements −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      IDictionary<int, int> d = new Dictionary<int, int>();
      d.Add(1, 97);
      d.Add(2, 89);
      d.Add(3, 77);
      d.Add(4, 88);
      d.Add(5, 78);
      d.Add(6, 98);
      Console.WriteLine("Total elements: " + d.Count);
   }
}

The output of the above code is −

Total elements: 6

Using ContainsKey() and ContainsValue()

These methods check for the existence of keys and values respectively −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Dictionary<string, int> ages = new Dictionary<string, int>();
      ages.Add("Alice", 25);
      ages.Add("Bob", 30);
      ages.Add("Charlie", 35);
      
      Console.WriteLine("Contains key 'Alice': " + ages.ContainsKey("Alice"));
      Console.WriteLine("Contains key 'David': " + ages.ContainsKey("David"));
      Console.WriteLine("Contains value 30: " + ages.ContainsValue(30));
      Console.WriteLine("Contains value 40: " + ages.ContainsValue(40));
   }
}

The output of the above code is −

Contains key 'Alice': True
Contains key 'David': False
Contains value 30: True
Contains value 40: False

Using TryGetValue() for Safe Access

The TryGetValue() method safely retrieves values without throwing exceptions if the key doesn't exist −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Dictionary<string, int> scores = new Dictionary<string, int>();
      scores.Add("Math", 95);
      scores.Add("Science", 88);
      scores.Add("English", 92);
      
      int value;
      if (scores.TryGetValue("Math", out value)) {
         Console.WriteLine("Math score: " + value);
      }
      
      if (scores.TryGetValue("History", out value)) {
         Console.WriteLine("History score: " + value);
      } else {
         Console.WriteLine("History score not found");
      }
   }
}

The output of the above code is −

Math score: 95
History score not found

Using Remove() and Clear()

The Remove() method removes individual elements, while Clear() removes all elements −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Dictionary<string, string> capitals = new Dictionary<string, string>();
      capitals.Add("USA", "Washington");
      capitals.Add("UK", "London");
      capitals.Add("France", "Paris");
      
      Console.WriteLine("Initial count: " + capitals.Count);
      
      capitals.Remove("UK");
      Console.WriteLine("After removing UK: " + capitals.Count);
      
      capitals.Clear();
      Console.WriteLine("After clearing all: " + capitals.Count);
   }
}

The output of the above code is −

Initial count: 3
After removing UK: 2
After clearing all: 0

Conclusion

Dictionary methods in C# provide efficient ways to manage key-value collections. Use Add() and Remove() for modifications, ContainsKey() and TryGetValue() for safe lookups, and Clear() for bulk operations. These methods make Dictionary a powerful data structure for fast key-based access.