HashSet in C# with Examples

How to Create a HashSet in C#

Creating a HashSet in C# is straightforward and involves the following steps:

Step 1: Import the Required Namespace

Before you can work with HashSets, make sure to include the System.Collections.Generic namespace in your code. This namespace contains the HashSet class.

Step 2: Declare and Initialize a HashSet

You can declare and initialize a HashSet by specifying its type (e.g., int, string, custom objects) and using the new keyword to create an instance of HashSet.

In this example, we've created an empty HashSet of integers. You can replace int with any other data type or class as needed.

Step 3: Add Elements to the HashSet

To populate your HashSet, you can use the Add method to insert elements. Each element is automatically checked for duplicates, ensuring that only unique values are stored.

In this code snippet, we've added two integers to the numbers HashSet, and the duplicate value 42 is automatically filtered out.

Now, you have a HashSet named numbers with unique elements. You can use various methods and operations to work with this HashSet, including adding, removing, and performing set operations like union, intersection, and difference.

Example

Output:

In this example, we created a HashSet of integers, added a few numbers, including a duplicate, and then printed the elements. As you can see in the output, only the unique values (42 and 17) are present in the HashSet. The duplicate 42 is automatically filtered out, demonstrating the HashSet's capability to ensure uniqueness.

Working With HashSet in C#

A HashSet in C# offers a wide range of methods and operations for managing collections of unique elements efficiently. In this section, we'll explore some essential operations, starting with adding elements to a HashSet and handling duplicate elements.

Attempt to Insert a Duplicate Element in a HashSet

One of the primary features of a HashSet is its ability to automatically reject duplicate elements. Let's see this in action with an example:

Output:

In this example, we've created a HashSet called colors to store unique color names. Notice that we attempted to add "Red" twice. However, when we iterate through the HashSet and print its elements, you'll see that only one "Red" is present. HashSet automatically filters out duplicate elements, ensuring that each element in the collection is unique.

This behavior is particularly valuable when you want to maintain a collection of distinct values without the overhead of manually checking for duplicates.

How to Remove Elements from the HashSet?

Removing elements from a HashSet is straightforward using the Remove method. Let's look at an example:

Output:

In this example, we've created a HashSet called numbers and added three integers to it. We then removed the element 10 using the Remove method. When we print the elements of the HashSet, you can see that 10 has been successfully removed.

These basic operations demonstrate the simplicity and power of HashSet in C# for managing collections of unique elements. In the upcoming sections, we'll explore more advanced set operations that HashSet offers, such as union, intersection, and difference.

Set Operations in HashSet

HashSet in C# provides a set of powerful set operations that allow you to combine, compare, and manipulate collections of unique elements. In this section, we will explore three fundamental set operations: UnionWith, IntersectWith, and ExceptWith.

UnionWith

The UnionWith method combines two HashSets, creating a new HashSet containing all the unique elements from both sets. Let's see an example:

Output:

In this example, we created two HashSets, set1 and set2, each containing unique integers. By using the UnionWith method, we combined set1 and set2, resulting in a new HashSet, set1, that contains all unique elements from both sets. The resulting set1 includes elements 1 through 6, with duplicates automatically removed.

IntersectWith

The IntersectWith method, on the other hand, finds the common elements between two HashSets and updates the first HashSet with these elements. Here's an example:

Output:

In this example, we have set1 and set2, each containing unique integers. Using the IntersectWith method, we found the common elements between the two sets, which are 3 and 4. set1 was then updated to only contain these common elements.

ExceptWith

The ExceptWith method subtracts the elements of one HashSet from another, modifying the first HashSet with the result. Here's an example:

Output:

In this example, we have set1 and set2, each containing unique integers. The ExceptWith method subtracts the elements in set2 from set1, resulting in set1 containing only the elements that are exclusive to it, which are 1 and 2.

These set operations in HashSet are invaluable for performing various tasks, such as combining, comparing, or filtering collections of unique elements, and simplifying complex operations in your C# programs.