Hashset

HashSet is a collection containing only unique elements.

Introduction

In order to use it, the following line needs to be added:

using System.Collections.Generic;

Syntax

HashSet<type> hashSetName = new HashSet<type>();

Inserting Data

Insertion is done via the Add function. Like in the following example:

using System; using System.Collections.Generic; namespace csharp { class Program { static void Main(string[] args) { HashSet<string> cities = new HashSet<string>(); cities.Add("Tokyo"); cities.Add("Chicago"); cities.Add("Tokyo"); cities.Add("Madrid"); foreach (string city in cities) { Console.Write(city + " "); } } } }

Output:

Tokyo Chicago Madrid

Notice that Tokyo is contained only once, since no duplicates are allowed.

Size

Size is the count of HashSet elements. It's accessed via the Count property.

using System; using System.Collections.Generic; namespace csharp { class Program { static void Main(string[] args) { HashSet<string> cities = new HashSet<string>(); cities.Add("Tokyo"); cities.Add("Chicago"); cities.Add("Tokyo"); cities.Add("Madrid"); Console.Write(cities.Count); } } }

Output:

3

Remove Element

Certain values can be removed via the remove function.

using System; using System.Collections.Generic; namespace csharp { class Program { static void Main(string[] args) { HashSet<string> names = new HashSet<string>(); names.Add("Emily"); names.Add("Lily"); names.Add("Teo"); names.Remove("Teo"); foreach (string name in names) { Console.Write(name + " "); } } } }

Output:

Emily Lily

Contains

A value can be checked if contained via the contains method.

using System; using System.Collections.Generic; namespace csharp { class Program { static void Main(string[] args) { HashSet<string> names = new HashSet<string>(); names.Add("Leo"); names.Add("Shone"); names.Add("Alice"); Console.WriteLine(names.Contains("Shone")); } } }

Output:

true

Loop Through

It can be iterated via for and for-each loop:

using System; using System.Collections.Generic; namespace csharp { class Program { static void Main(string[] args) { HashSet<string> makes = new HashSet<string>(); makes.Add("Volvo"); makes.Add("Ford"); makes.Add("Audi"); foreach (string make in makes) { Console.Write(make + " "); } } } }

Output:

Volvo Ford Audi