Collections in .NET

The .NET framework provides a rich set of collection types that simplify data storage, retrieval, and manipulation. Whether you need a dynamic list, a key‑value map, or a thread‑safe queue, .NET has a collection tailored to your scenario.

When to Use Which Collection?

Scenario	Recommended Collection	Key Features
Ordered, index‑based access	`List<T>`	Dynamic resizing, fast random access
Key‑value lookup	`Dictionary<K,V>`	O(1) lookups, unique keys
Fixed size, contiguous memory	`Array`	Fast iteration, low overhead
First‑in‑first‑out processing	`Queue<T>`	Enqueue/Dequeue O(1)
Last‑in‑first‑out processing	`Stack<T>`	Push/Pop O(1)
Data binding & UI updates	`ObservableCollection<T>`	Change notifications

Common Operations

// Create a list
var numbers = new List<int> { 1, 2, 3 };

// Add an element
numbers.Add(4);

// Remove by value
numbers.Remove(2);

// Iterate
foreach (var n in numbers)
{
    Console.WriteLine(n);
}

// Dictionary example
var ages = new Dictionary<string, int>();
ages["Alice"] = 30;
ages["Bob"] = 25;
Console.WriteLine(ages["Alice"]);

Performance Tips

Prefer List<T> over ArrayList for type safety and better performance.
When the collection size is known and unchanged, use an Array to reduce allocation overhead.
For large datasets that require frequent lookups, Dictionary<K,V> provides constant‑time access.
Use ReadOnlyCollection<T> or IReadOnlyList<T> to expose data without allowing modifications.

Collections in .NET

When to Use Which Collection?

Common Operations

Performance Tips

Further Reading