How to Get Hashtable Elements as Sorted Array?

A Hashtable is a non-generic collection of key-value pairs that are arranged according to the hash code of the key. The hashtable optimizes lookups by calculating the hash code of each key and storing it internally. When accessing a particular value, this hash code is matched with the specified key.

This hashtable collection is defined in the System.Collections namespace of C#. The class that represents the hashtable collection is the Hashtable class. By default, hashtable collections are unsorted. To get sorted data, we need to extract the elements into an Array and sort them.

Why Hashtables Are Unsorted

Hashtables store elements based on hash codes for optimal performance. The insertion order and natural sorting are not maintained because elements are placed in buckets determined by their hash values, not their actual content order.

Approach to Get Sorted Array

To get hashtable elements as a sorted array, follow these steps

• Create a Hashtable object and populate it with key-value pairs

• Create a string array with length equal to the hashtable count

• Iterate through the hashtable and copy keys or values to the array

• Sort the array using Array.Sort()

Using Hashtable Keys for Sorting

Example

using System;
using System.Collections;

class Program {
   public static void Main() {
      // Create a Hashtable
      Hashtable langCodes = new Hashtable();

      // Add elements to the Hashtable
      langCodes.Add("C++", "CPlusPlus");
      langCodes.Add("C#", "CSharp");
      langCodes.Add("Java", "Java");
      langCodes.Add("PL", "Perl");
      langCodes.Add("PG", "Prolog");

      // Create array of length = hashtable length
      string[] sortedArray = new string[langCodes.Count];

      // Retrieve key values in Array
      int i = 0;
      Console.WriteLine("Hashtable langCodes Contents:");
      foreach (DictionaryEntry de in langCodes) {
         Console.WriteLine("{0} ({1})", de.Key, de.Value);
         sortedArray[i] = de.Key.ToString();
         i++;
      }

      Array.Sort(sortedArray);
      Console.WriteLine("\nContents of sorted array based on Hashtable keys:");
      foreach (var item in sortedArray) {
         Console.WriteLine(item);
      }
   }
}

The output of the above code is

Hashtable langCodes Contents:
PG (Prolog)
Java (Java)
C# (CSharp)
PL (Perl)
C++ (CPlusPlus)

Contents of sorted array based on Hashtable keys:
C#
C++
Java
PG
PL

Using Hashtable Values for Sorting

Example

using System;
using System.Collections;

class Program {
   public static void Main() {
      // Create a Hashtable
      Hashtable numberNames = new Hashtable();

      // Add elements to the Hashtable
      numberNames.Add(12, "Twelve");
      numberNames.Add(2, "Two");
      numberNames.Add(65, "Sixty Five");
      numberNames.Add(15, "Fifteen");
      numberNames.Add(18, "Eighteen");

      // Create array of length = hashtable length
      string[] sortedArray = new string[numberNames.Count];

      // Retrieve hashtable values in array
      int i = 0;
      Console.WriteLine("Hashtable numberNames Contents:");
      foreach (DictionaryEntry de in numberNames) {
         Console.WriteLine("{0} ({1})", de.Key, de.Value);
         sortedArray[i] = de.Value.ToString();
         i++;
      }

      Array.Sort(sortedArray);
      Console.WriteLine("\nContents of sorted array based on Hashtable values:");
      foreach (var item in sortedArray) {
         Console.WriteLine(item);
      }
   }
}

The output of the above code is

Hashtable numberNames Contents:
18 (Eighteen)
12 (Twelve)
65 (Sixty Five)
2 (Two)
15 (Fifteen)

Contents of sorted array based on Hashtable values:
Eighteen
Fifteen
Sixty Five
Twelve
Two

Alternative Approach Using LINQ

You can also use LINQ to get sorted keys or values more concisely

Example

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

class Program {
   public static void Main() {
      Hashtable langCodes = new Hashtable();
      langCodes.Add("C++", "CPlusPlus");
      langCodes.Add("C#", "CSharp");
      langCodes.Add("Java", "Java");
      langCodes.Add("Python", "Python");

      // Get sorted keys using LINQ
      var sortedKeys = langCodes.Keys.Cast<string>().OrderBy(x => x).ToArray();

      Console.WriteLine("Sorted keys using LINQ:");
      foreach (var key in sortedKeys) {
         Console.WriteLine(key);
      }

      // Get sorted values using LINQ
      var sortedValues = langCodes.Values.Cast<string>().OrderBy(x => x).ToArray();

      Console.WriteLine("\nSorted values using LINQ:");
      foreach (var value in sortedValues) {
         Console.WriteLine(value);
      }
   }
}

The output of the above code is

Sorted keys using LINQ:
C#
C++
Java
Python

Sorted values using LINQ:
CSharp
CPlusPlus
Java
Python

Conclusion

While Hashtable collections are inherently unsorted for performance reasons, you can extract their elements into arrays and sort them using Array.Sort() or LINQ methods. This approach allows you to work with sorted data while maintaining the fast lookup benefits of hashtables for the original collection.