Collections in C#: List, Dictionary, and HashSet

Collections are essential in C# for storing and manipulating groups of data. In this guide, you'll explore three common collection types in C#: List, Dictionary, and HashSet. These collections serve different purposes and have unique characteristics.

List<T>

The `List` is a dynamic array that can store elements of a specific type. It provides flexibility for adding, removing, and accessing elements in a list.

Example of using a `List`:

using System;
using System.Collections.Generic;
class Program
{
    static void Main()
    {
        List<int> numbers = new List<int>();
        // Adding elements
        numbers.Add(1);
        numbers.Add(2);
        numbers.Add(3);
        // Accessing elements
        int firstNumber = numbers[0]; // 1
        int lastNumber = numbers[numbers.Count - 1]; // 3
        // Removing elements
        numbers.Remove(2); // Removes the value 2 from the list
        // Iterating through the list
        foreach (int number in numbers)
        {
            Console.WriteLine(number);
        }
    }
}
    

Dictionary<TKey, TValue>

The `Dictionary` is a key-value pair collection where each element is associated with a unique key. It's useful for fast lookups based on the key.

Example of using a `Dictionary`:

using System;
using System.Collections.Generic;
class Program
{
    static void Main()
    {
        Dictionary<string, int> ages = new Dictionary<string, int>();
        // Adding key-value pairs
        ages["Alice"] = 30;
        ages["Bob"] = 25;
        // Accessing values by key
        int aliceAge = ages["Alice"]; // 30
        // Checking for key existence
        bool hasKey = ages.ContainsKey("Bob"); // true
        // Iterating through key-value pairs
        foreach (var kvp in ages)
        {
            Console.WriteLine($"Name: {kvp.Key}, Age: {kvp.Value}");
        }
    }
}
    

HashSet<T>

The `HashSet` is an unordered collection of unique elements. It's suitable for tasks that require checking for duplicate values.

Example of using a `HashSet`:

using System;
using System.Collections.Generic;
class Program
{
    static void Main()
    {
        HashSet<string> colors = new HashSet<string>();
        // Adding elements
        colors.Add("Red");
        colors.Add("Green");
        colors.Add("Blue");
        // Adding a duplicate (ignored)
        colors.Add("Red");
        // Checking for element existence
        bool hasGreen = colors.Contains("Green"); // true
        bool hasYellow = colors.Contains("Yellow"); // false
        // Iterating through elements
        foreach (string color in colors)
        {
            Console.WriteLine(color);
        }
    }
}
    

Conclusion

Collections play a vital role in C# programming, and you've explored three essential collection types: List, Dictionary, and HashSet. Each collection serves distinct purposes and provides unique capabilities to help you manage and manipulate data effectively.

Practice using these collections in your C# programs to become proficient in data manipulation. As you continue your programming journey, you'll discover more advanced collection types and scenarios for their usage.