# Introduction

To start your journey in mastering R, the following six chapters will help you learn the foundational components of R. I expect that you’ve already seen many of these pieces before, but you probably have not studied them deeply. To help check your existing knowledge, each chapter starts with a quiz; if you get all the questions right, feel free to skip to the next chapter!

1. Chapter 2 teaches you about an important distinction that you probably haven’t thought deeply about: the difference between an object and its name. Improving your mental model here will help you make better predictions about when R copies data and hence which basic operations are cheap and which are expensive.

2. Chapter 3 dives into the details of vectors, helping you learn how the different types of vector fit together. You’ll also learn about attributes, which allow you to store arbitrary metadata, and form the basis for two of R’s object-oriented programming toolkits.

3. Chapter 4 describes how to use subsetting to write clear, concise, and efficient R code. Understanding the fundamental components will allow you to solve new problems by combining the building blocks in novel ways.

4. Chapter 5 presents tools of control flow that allow you to only execute code under certain conditions, or to repeatedly execute code with changing inputs. These include the important if and for constructs, as well as related tools like switch() and while.

5. Chapter 6 deals with functions, the most important building blocks of R code. You’ll learn exactly how they work, including the scoping rules, which govern how R looks up values from names. You’ll also learn more of the details behind lazy evaluation, and how you can control what happens when you exit a function.

6. Chapter 7 describes a data structure that is crucial for understanding how R works, but quite unimportant for data analysis: the environment. Environments are the data structure that binds names to values, and they power important tools like package namespaces. Unlike most programming languages, environments in R are “first class” which means that you can manipulate them just like other objects.

7. Chapter 8 concludes the foundations of R with an exploration of “conditions”, the umbrella term used to describe errors, warnings, and messages. You’ve certainly encountered these before, so in this chapter you learn how to signal them appropriately in your own functions, and how to handle them when signalled elsewhere.