Hashset

Description

HashSet collection contains a group of elements of unique values stored at respective indexes.

HashSet<T> referenceVariable = new HashSet<T>();

Full Path: System.Collections.Generic.HashSet
The HashSet class is a generic class.
You can't set/get the element based on the key/index.
Searches elements based on the index generated from the search value.
HashSet allows only one null value, while Hashtable allows only one null key and multiple null values.
You can't access elements based on key/index (Use the Contains method to search for an element).
You can't sort elements in HashSet.
Elements must be unique; duplicate elements are not allowed.

Example:

HashSet<string> messages = new HashSet<string>()
{
    "Good Morning", "How Are You", "Have a good day"
};

foreach (string message in messages) {
    Console.WriteLine(message);
}

Process of Adding an Element

Generate index based on the value (Example: index = hash code % count)
Add the element (value) next to the linked list at the generated index.

Features

Overview

Feature	Description
`Count`	Returns count of elements.
`void Add(T value)`	Adds an element (key/value pair).
`void Remove(T value)`	Removes an element based on specified key.
`void RemoveWhere(Predicate)`	Removes elements that match a condition.
`bool Contains(T value)`	Determines whether the specified value exists.
`void Clear()`	Removes all elements.
`void UnionWith(IEnumerable<T>)`	Unions the hashset and the specified collection.
`void IntersectWith(IEnumerable<T>)`	Intersects the hashset and the specified collection.

Info

All the shared features can be used for HashSet

RemoveWhere

It allows remove all elements from the collection that satisfy a specified condition. The condition is expressed using a predicate (a function delegate that returns a boolean).

Example:

messages.RemoveWhere(m => m.EndsWith("You"));

UnionWith

Is used to modify the current set to be the union of the current set and a specified collection. It adds all unique elements from the provided collection to the HashSet, ensuring no duplicates.

Example:

// Create two HashSets
HashSet<string> employees2021 = new HashSet<string>() { "Amar", "Akhil", "Samareen" };
HashSet<string> newEmployees2022 = new HashSet<string>() { "John", "Scott", "Smith", "David" };

// Union
employees2021.UnionWith(newEmployees2022);

IntersectWith

Is used to modify the current HashSet<T> by retaining only the elements that are also present in a specified collection. It performs a mathematical set intersection, which means that the resulting set contains only the common elements from both sets. This method is useful when narrowing down a collection to shared elements.

Example:

// Create two HashSets
HashSet<string> employees2021 = new HashSet<string>() { "Amar", "Akhil", "Samareen" };
HashSet<string> employees2022 = new HashSet<string>() { "John", "Scott", "Amar", "Akhil", "Smith", "David" };

// Use IntersectWith
employees2021.IntersectWith(employees2022);