Dictionary Class in C#

Dictionary in C# is a collection of keys and values. It is a generic collection class in the System.Collection.Generics namespace.

Syntax

Following is the syntax −

public class Dictionary<TKey,TValue>

Above, the key parameter is the type of keys in the dictionary, whereas TValue is the type of values.

Example

Let us now create a Dictionary and add some elements −

using System;
using System.Collections.Generic;
public class Demo {
   public static void Main(){
      Dictionary<string, string> dict = new Dictionary<string, string>();
      dict.Add("One", "John");
      dict.Add("Two", "Tom");
      dict.Add("Three", "Jacob");
      dict.Add("Four", "Kevin");
      dict.Add("Five", "Nathan");
      Console.WriteLine("Key/value pairs...");
      foreach(KeyValuePair<string, string> res in dict){
         Console.WriteLine("Key = {0}, Value = {1}", res.Key, res.Value);
      }
   }
}

Output

This will produce the following output −

Key/value pairs...
Key = One, Value = John
Key = Two, Value = Tom
Key = Three, Value = Jacob
Key = Four, Value = Kevin
Key = Five, Value = Nathan

Example

Now, let us see an example and remove some keys −

using System;
using System.Collections.Generic;
public class Demo {
   public static void Main(){
      Dictionary<string, string> dict = new Dictionary<string, string>();
      dict.Add("One", "Kagido");
      dict.Add("Two", "Ngidi");
      dict.Add("Three", "Devillers");
      dict.Add("Four", "Smith");
      dict.Add("Five", "Warner");
      Console.WriteLine("Count of elements = "+dict.Count);
      Console.WriteLine("Removing some keys...");
      dict.Remove("Four");
      dict.Remove("Five");
      Console.WriteLine("Count of elements (updated) = "+dict.Count);
      Console.WriteLine("
Key/value pairs...");
      foreach(KeyValuePair<string, string> res in dict){
         Console.WriteLine("Key = {0}, Value = {1}", res.Key, res.Value);
      }
      Console.Write("
All the keys..
");
      Dictionary<string, string>.KeyCollection allKeys = dict.Keys;
      foreach(string str in allKeys){
         Console.WriteLine("Key = {0}", str);
      }
   }
}

Output

This will produce the following output −

Count of elements = 5
Removing some keys...
Count of elements (updated) = 3
Key/value pairs...
Key = One, Value = Kagido
Key = Two, Value = Ngidi
Key = Three, Value = Devillers
All the keys..
Key = One
Key = Two
Key = Three