Chapter 12 Functions

Learning Objectives

After completing this chapter, you will be able to:

• Define custom functions with arguments and default values
• Understand variable scoping and how R searches for variables
• Write anonymous functions for concise, one-off operations
• Use ... (dot-dot-dot) to pass additional arguments flexibly

In theory, you can already write very complicated codes, accomplishing a lot of data analysis tasks. In this chapter, you will learn a very powerful tool, functions.

At a glance – Chapter ROADMAP Section 12.1. Defining Functions: Learn to create custom, reusable blocks of code with arguments and return values.
Section 12.2 & Section 12.3. Advanced Concepts: Master anonymous functions, nested functions, and understand variable scoping rules in R.
Section 12.4. Functional Programming: Use the apply family and purrr for cleaner, more efficient iteration over lists and data frames.
Section 12.5. Robustness: Implement tryCatch() and other tools to handle errors and warnings gracefully.

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