Appendix B — Glossary

A quick reference for terms used throughout this course, in alphabetical order. If you come across a word you don’t recognise while working through a session, check here first.

Console: The pane in RStudio where you type R code directly and see results immediately, without saving it to a file. Introduced in Overview of R and RStudio.
CRAN (Comprehensive R Archive Network): The main online repository of R packages. When you run install.packages(), R usually downloads the package from CRAN. See R Packages and Libraries.
Data frame: A table-like data structure where each column is a variable (and can be a different type) and each row is an observation – similar to a spreadsheet. See Data Frames and Lists.
Environment: The current collection of objects (variables, data frames, functions, etc.) that R has stored in memory for your session. Visible in RStudio’s Environment pane. See Overview of R and RStudio.
Factor: A data structure used to represent categorical data. A factor stores its values as a fixed set of categories, called levels. See Vectors and Factors.
Function: A reusable piece of code that performs a specific task, e.g. c(), mean(), or read_csv(). Functions take arguments (inputs) inside parentheses and usually return a result.
Level: One of the distinct categories that a factor can take. For example, a factor for “fruit type” might have the levels “Apple”, “Banana”, and “Cherry”. See Vectors and Factors.
Library: The folder on your computer where installed R packages are stored. Load a package from your library into your session with library(). See R Packages and Libraries.
List: A flexible data structure that can hold elements of different types and lengths – including other lists (a nested list). Access elements with [[ ]] or $. See Data Frames and Lists.
Object: A general term for anything stored in R’s environment – a number, a vector, a data frame, a function, and so on. Every object has a name (its variable) and a value.
Package: A bundle of functions, data, and documentation that extends R’s capabilities, e.g. ggplot2 or readr. Install once with install.packages(), then load each session with library(). See R Packages and Libraries.
Script: A plain-text file (.R) containing only R code, with no narrative text. Compare with R Markdown. See R Markdown Basics.
Variable: The name you give to an object so you can refer to it later, e.g. my_number in my_number <- 10. Created with the assignment operator <-. See Basic R Syntax and Operations.
Vector: An ordered collection of values that are all the same type (e.g. all numeric, or all character), created with c(). The most basic data structure in R. See Vectors and Factors.
Working directory: The folder on your computer that R treats as its “home base” for the current session – relative file paths (like "data/file.csv") are interpreted relative to this folder. Check it with getwd() and set it with setwd(). See R Markdown Basics.