Documentation

Lambdas

A lambda expression is an expression that returns a method. Very useful for searching arrays/objects.

Here is a useful piece of code to select files from a directory that is over a certain number of days.
var files = Directory.GetFiles(path).Select(file => new FileInfo(file)).Where (file => file.LastWriteTime < DateTime.Now.AddDays(-1* _numberOfDaysBeforeDelete)).ToList();
and here is how we can simply remove the above files
files.ForEach(file => file.Delete());

SELECT
Code here creates a list of integers and uses the List method fo FindIndex to find integers that do not have a modulus of 2. The lambda expression returns a method of oddIndex.

List<int> elements = new List<int>() { 10, 20, 31, 40 };
// ... Find index of first odd element.
int oddIndex = elements.FindIndex(x => x % 2 != 0);
Console.WriteLine(oddIndex);
Returns 31

FUNCTION
Starts with “FUNC”, include parameters and return type ,
function name “AddVat”, “=”,
input parameters (x, y),
lambda code “=>”
function code “x * ( 1 + (y / 100));
Console.WriteLine(“Cost + Vat = {AddVat(55,20)});

Func AddVat = (x, y) => x * (1 + (y / 100));
lstPeople.Items.Add(AddVat(55, 20));
Returns 66.

ACTION
An action does not return anything. It can have parameters.
Action value = () => Console.WriteLine("Hi, friend");
value.Invoke();

DELEGATE
Used for anonymous functions.
Func<int, int> test1 = delegate (int x) { return x + 1; };
Console.WriteLine(test1.Invoke(10));

LISTS