What Is List and HashSet Data Structure in C#?

Lists and HashSets are two commonly used data structures in the C# programming language. In this tutorial, we will explore what these data structures are and how they can be used effectively in your C# programs.

Lists

A list is an ordered collection of elements, where each element has an index associated with it. Lists in C# are represented by the List class, which is part of the System.Collections.Generic namespace.

To use a List, you first need to declare and initialize it:

List<T> myList = new List<T>();

The T in the declaration denotes the type of elements that the list will hold. For example, if you want to create a list of integers, you would replace T with int:

List<int> numbers = new List<int>();

You can then add elements to the list using the Add() method:

numbers.Add(10);
numbers.Add(20);
numbers.Add(30);

To access an element in the list, you can use indexing:

int firstElement = numbers[0]; // Returns 10
int secondElement = numbers[1]; // Returns 20
int thirdElement = numbers[2]; // Returns 30

You can also modify elements in a list by assigning a new value to a specific index:

numbers[1] = 25; // Modifies the second element from 20 to 25

In addition to these basic operations, lists provide various methods for manipulation, such as Remove() to remove an element, Count property to get the number of elements, and Contains() to check if a specific element exists in the list. Lists are versatile and can be used in a wide range of scenarios.

HashSets

A HashSet is an unordered collection of unique elements. In other words, it does not allow duplicate values. HashSets in C# are represented by the HashSet class, also part of the System.

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

mySet.Add(10);
mySet.Add(20);
mySet.Add(30);
mySet.Add(10); // Ignored since duplicates are not allowed

bool containsTen = mySet.Contains(10); // Returns true
bool containsFifty = mySet.Contains(50); // Returns false

mySet.Remove(20);