C# Collections

List vs ArrayList

Don’t use ArrayList. Use List<T> instead. ArrayList comes from times when C# didn’t have generics and it’s not the same ArrayList we have in Java.

DON’T

ArrayList array = new ArrayList();
array.Add(1);
array.Add("Pony"); // Later error at runtime if you try to operate with numbers.

do

List<int> list = [];
list.Add(1);
list.Add("Pony"); // Compilation error.

retrieve data

List<string> list = [ "yes", "no"];
var firstItem = list[0];

Tuples

Tuples help us manipulate data sets easily without having to define a new class with custom properties.

One of its benefits is that they can be used as method params and return types.

// simple tuple
(int, string) employee = (23, "Yohannes");
Console.WriteLine($"{employee.Item2} is {employee.Item1} years old");

// tuple with named parameters
(int Age, string Name) employee2 = (29, "Ramon");
Console.WriteLine($"{employee2.Name} is {employee2.Age} years old");

// nested tuples
var employees = ((23, "Yohannes"), (29, "Ramon"));
Console.WriteLine(employees.Item1); // (23, "Yohannes")
Console.WriteLine(employees.Item1.Item1); // 23

Tuples as function params

We can also use tuples as params for functions.

public void GetEmployee((string Name, int Age) employee)
{
	Console.WriteLine($"{employee.Name} is {employee.Age} years old");
}

// call it as such
GetEmployee(("Yohannes", 23));

Tuples as the return type

public (string Name, int Age) GetEmployee()
{
	return ("Yohannes", 23);
}

var emp = GetEmployee();
Console.WriteLine($"{emp.Name}, {emp.Age}");

Dictionary

Dictionaries are preferred over Hashtables, as they include type safety through generics.

var dc = new Dictionary<string,string>();
string key = "txt";
dc.Add(key, "hello world");

// easy way to access a dict value
string value2 = dc[key];

// better way
if(dc.TryGetValue(key, out var valor)) 
{
	Console.WriteLine(valor); // hello world
	dc[key] = "update key with new value";
} else 
{
	// key wasn't found in dictionary
	dc[key] = "insert as key didn't exist"
}

Hashtable (don’t - use Dictionaries)

Hashtable table = new Hashtable();
table.Add("Alex", 2.34);
var valor = table["Alex"];

Stack

Colección LIFO (Last in, First Out). Pensar en una pila de platos. El último plato que ponemos es el primero en salir.

Stack pila = new Stack();
pila.Push(1);
var numero = pila.Pop();

Queue

Coleccion FIFO (First in, First Out). Pensar en una cola para un evento. El primero que llegó es el primero que entra.

Queue cola = new Queue();
cola.Enqueue(3);
var numero = cola.Dequeue();

Reference(s)

https://www.syncfusion.com/blogs/post/working-with-tuple-in-csharp