C# program to get the List of keys from a Dictionary

In C#, you can extract all the keys from a Dictionary as a List using the Keys property. This is useful when you need to work with dictionary keys as a separate collection or perform operations like sorting, filtering, or iteration.

Syntax

Following is the syntax to get keys from a Dictionary −

Dictionary<TKey, TValue> dictionary = new Dictionary<TKey, TValue>();
List<TKey> keys = new List<TKey>(dictionary.Keys);

You can also use LINQ to convert keys to a List −

List<TKey> keys = dictionary.Keys.ToList();

Using Dictionary.Keys Property

The Keys property returns a collection of all keys in the dictionary. We can convert this collection to a List for easier manipulation −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Dictionary<int, string> d = new Dictionary<int, string>();
      
      // dictionary elements
      d.Add(1, "One");
      d.Add(2, "Two");
      d.Add(3, "Three");
      d.Add(4, "Four");
      d.Add(5, "Five");
      d.Add(6, "Six");
      d.Add(7, "Seven");
      d.Add(8, "Eight");
      
      // getting keys
      List<int> keys = new List<int>(d.Keys);
      Console.WriteLine("Displaying keys...");
      foreach (int res in keys) {
         Console.WriteLine(res);
      }
   }
}

The output of the above code is −

Displaying keys...
1
2
3
4
5
6
7
8

Using LINQ ToList() Method

You can also use LINQ's ToList() method to convert the keys collection directly to a List −

using System;
using System.Collections.Generic;
using System.Linq;

public class Demo {
   public static void Main() {
      Dictionary<string, int> scores = new Dictionary<string, int>() {
         {"Alice", 95},
         {"Bob", 87},
         {"Charlie", 92},
         {"Diana", 98}
      };
      
      // getting keys using LINQ
      List<string> playerNames = scores.Keys.ToList();
      
      Console.WriteLine("Player Names:");
      foreach (string name in playerNames) {
         Console.WriteLine("- " + name);
      }
      
      Console.WriteLine("\nTotal Players: " + playerNames.Count);
   }
}

The output of the above code is −

Player Names:
- Alice
- Bob
- Charlie
- Diana

Total Players: 4

Working with Different Key Types

This approach works with any key type. Here's an example using string keys and custom object values −

using System;
using System.Collections.Generic;

public class Product {
   public string Name { get; set; }
   public double Price { get; set; }
}

public class Demo {
   public static void Main() {
      Dictionary<string, Product> inventory = new Dictionary<string, Product>();
      
      inventory.Add("P001", new Product { Name = "Laptop", Price = 999.99 });
      inventory.Add("P002", new Product { Name = "Mouse", Price = 25.50 });
      inventory.Add("P003", new Product { Name = "Keyboard", Price = 75.00 });
      
      // getting product codes (keys)
      List<string> productCodes = new List<string>(inventory.Keys);
      
      Console.WriteLine("Product Codes in Inventory:");
      foreach (string code in productCodes) {
         Console.WriteLine(code);
      }
   }
}

The output of the above code is −

Product Codes in Inventory:
P001
P002
P003

Comparison of Methods

Conclusion

Getting keys from a Dictionary in C# is straightforward using either the List constructor with dictionary.Keys or LINQ's ToList() method. Both approaches create a separate List that you can manipulate independently from the original Dictionary. The constructor approach is slightly more efficient and doesn't require additional namespace imports.