Adding a Range of Elements to a HashSet in C#

In C#, the HashSet<T> class is an efficient data structure for managing unique elements. However, unlike some other collections, it does not have a built-in AddRange method. Instead, elements must be added one at a time using the Add method. This article explains how to add multiple elements to a HashSet using workarounds and best practices, with practical examples.

Adding Multiple Elements to a HashSet

Using a Loop to Add Elements

The simplest way to add a range of elements to a HashSet is by looping through the items and adding them one by one.

using System;
using System.Collections.Generic;

public class HashSetAddRangeExample
{
    public static void Main()
    {
        // Create a new HashSet of integers
        HashSet<int> numbers = new HashSet<int> { 1, 2, 3 };

        // Create an array of new numbers to add
        int[] newNumbers = { 4, 5, 6, 2 }; // Contains a duplicate (2)

        // Add each number to the HashSet individually
        foreach (int number in newNumbers)
        {
            numbers.Add(number);
        }

        // Display the updated set
        Console.WriteLine("Updated HashSet:");
        foreach (int number in numbers)
        {
            Console.WriteLine(number);
        }
    }
}

Using UnionWith for Sets

If you are working with another collection that is also a set, such as another HashSet, you can use the UnionWith method. It adds all elements from another set into the current HashSet.

using System;
using System.Collections.Generic;

public class HashSetUnionWithExample
{
    public static void Main()
    {
        // Create the original HashSet
        HashSet<string> fruits = new HashSet<string> { "Apple", "Banana", "Orange" };

        // Create another set of fruits to add
        HashSet<string> newFruits = new HashSet<string> { "Pineapple", "Mango", "Banana" }; // Contains a duplicate ("Banana")

        // Use UnionWith to add the new fruits
        fruits.UnionWith(newFruits);

        // Display the updated set
        Console.WriteLine("Updated HashSet:");
        foreach (string fruit in fruits)
        {
            Console.WriteLine(fruit);
        }
    }
}

Practical Applications

Bulk Data Import: Quickly import and deduplicate bulk data from another collection or file.
Set Operations: Use UnionWith, IntersectWith, and ExceptWith to manipulate multiple sets.

Best Practices for Adding Ranges to HashSet

Use Efficient Structures: When adding from other collections, convert them to a set-like structure first.
Check Duplicates: Ensure that you are aware of how duplicates are handled, especially if combining large collections.

Conclusion

Adding multiple elements to a HashSet requires thoughtful handling since there isn't an AddRange method. By using loops or set operations like UnionWith, you can efficiently incorporate large numbers of items while maintaining unique collections.

c# hashset addrange