Hands-On Programming with R

Appendix E. Debugging R Code

Note

This appendix refers to environments, the topic of Chapter 6, and uses examples from Chapter 7 and Chapter 8. You should read through these chapters first to get the most out of this appendix.

R comes with a simple set of debugging tools that RStudio amplifies. You can use these tools to better understand code that produces an error or returns an unexpected result. Usually this will be your own code, but you can also examine the functions in R or one of its packages.

Debugging code can take as much creativity and insight as writing code. There is no guarantee that you will find a bug or be able to fix it when you do. However, you can help yourself by using R’s debugging tools. These include the traceback, browser, debug, debugonce, trace, and recover functions.

Using these tools is usually a two-step process. First, you locate where an error occurred. Then you try to determine why it occurred. You can do the first step with R’s traceback function.

traceback

The traceback tool pinpoints the location of an error. Many R functions call other R functions, which call other functions, and so on. When an error occurs, it may not be clear which of these functions went wrong. Let’s consider an example. The following functions call one another, and the last function creates an error (you’ll see why in a second):

first <- function() second()
second <- function() third()
third <- function() fourth()
fourth <- function() fifth()
fifth <- function() bug ...