C# Foundations·C# from first file to first API

Collections and LINQ

LINQ turns filtering and shaping collections into readable pipelines.

Beginner 14 min read Lesson 8 of 300 Challenge included

What you will be able to do

Use Dictionary for lookup by key; do not scan a list repeatedly.
Prefer Any() over Count() > 0 when you only need existence.
Materialize with ToList only when you need a concrete list.

In plain English

List and Dictionary cover most day-to-day storage. LINQ adds composition: Where, Select, OrderBy and GroupBy. A LINQ query is not executed until you enumerate it, so keep the pipeline close to the use site.

Linq.csC#

var lessons = new[]
{
    new { Title = "CSS Grid", Minutes = 16 },
    new { Title = "Flexbox", Minutes = 15 },
    new { Title = "Semantic HTML", Minutes = 13 },
};

var shortLessons = lessons
    .Where(lesson => lesson.Minutes <= 15)
    .OrderBy(lesson => lesson.Minutes)
    .Select(lesson => lesson.Title)
    .ToList();

var total = lessons.Sum(lesson => lesson.Minutes);

Your turn

Filter and sort

Medium

Given a list of lessons with Minutes, keep those under 15 minutes and order them ascending.

CSHARP · starter

var result = lessons;

Check your understanding before moving on.

Knowledge checkQuestion 1

Which method checks whether any item matches without counting the whole collection?

Select an answer to continue

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Lesson 8 of 300 · 0% of course