LINQ

LINQ (Language Integrated Query) filters, transforms, and aggregates any collection through a uniform, chainable API — C#'s equivalent of Java's streams.

List<string> names = new() { "Ada", "Bob", "Grace", "Al" };

var longNames = names
    .Where(name => name.Length > 2)
    .Select(name => name.ToUpper())
    .OrderBy(name => name)
    .ToList();

Console.WriteLine(string.Join(", ", longNames)); // ADA, GRACE

LINQ also has an alternate query syntax, resembling SQL, equivalent to the method-chain style above:

var result = from name in names
             where name.Length > 2
             orderby name
             select name.ToUpper();

Common mistakes

• Enumerating a LINQ query multiple times without realizing it re-runs the whole pipeline each time (LINQ is lazy, like a Java stream) — call .ToList() once if the result is needed more than once.

Practice

Given List<int> nums = new() { 1, 2, 3, 4, 5, 6 };, use LINQ to produce a list of only the even numbers, doubled.

var result = nums
    .Where(n => n % 2 == 0)
    .Select(n => n * 2)
    .ToList();
// { 4, 8, 12 }