Debugging

Debugging is the process of finding and fixing errors in your code. R provides a few tools to help with this:

• browser(): This function stops the execution of your code and puts you in “debugging mode”.
• debug(): You can use this function to step through the execution of a function one line at a time.
• traceback(): This function displays a stack trace of all the function calls leading up to the error.

Here’s an example of how you might use these tools:

troubled_function <- function() {
  x <- log("a")
  return(x)
}

debug(troubled_function)
troubled_function()

When you run this code, R will pause at the beginning of troubled_function(), and you can step through the function one line at a time by pressing Enter.

Understanding and effectively leveraging R’s error handling and debugging tools can greatly speed up the process of writing and refining your code.

Using Traceback

The traceback() function is particularly useful for understanding the sequence of events that led to an error. When you run traceback() immediately after an error occurs, it shows you the sequence of function calls that led up to the error.

Consider the following example:

f1 <- function() {
  f2()
}

f2 <- function() {
  f3()
}

f3 <- function() {
  log("a")
}

f1()
traceback()

In this case, traceback() would show you that the error occurred in f3(), which was called by f2(), which was called by f1().

Using recover

R provides an interactive debugging tool, recover(). When an error occurs, recover() gives you the opportunity to modify the error and resume computation. You can access recover() by setting options(error = recover).

Here’s an example:

options(error = recover)

f1 <- function() {
  f2()
}

f2 <- function() {
  f3()
}

f3 <- function() {
  log("a")
}

f1()

Running this code will give you an interactive menu where you can choose which environment to enter and modify the error.

Debugging with RStudio

RStudio, a popular integrated development environment (IDE) for R, also provides several helpful debugging tools. These include:

• Breakpoints: You can set breakpoints at any line of your code. When R reaches a breakpoint, it enters the browser, allowing you to inspect the current state of the values and step through your code.
• Rerun with Debug: This is a function that allows you to rerun previous commands with debugging.
• Debugging pane: This pane displays the call stack, which is the sequence of function calls that led up to the current position.

These features can make the debugging process more visual and interactive.