Errors and bugs happen when writing code, especially for beginners. R provides tools to help find and fix these errors. This tutorial will teach you how to handle errors and debug your code in R, step by step, using simple explanations and practical examples.

1. Types of Errors in R

Errors in R usually fall into three categories:

1.1 Syntax Errors

  • These happen when R doesn’t understand your code because of a mistake in writing.
  • Example: print("Hello) # Missing closing quote
  • Fix: Ensure you write complete and correct commands.

1.2 Runtime Errors

  • These occur while the code is running, even if it was written correctly.
  • Example: x <- 10 / 0 # Division by zero
  • Fix: Avoid operations that break mathematical rules, like dividing by zero.

1.3 Logical Errors

  • The code runs without crashing, but gives the wrong result.
  • Example: mean(c(1, 2, 3, 4, 5, NA)) # Missing argument to handle NA values
  • Fix: Use na.rm = TRUE to ignore missing values: mean(c(1, 2, 3, 4, 5, NA), na.rm = TRUE)

2. Handling Errors in R

2.1 Using try()

  • Prevents code from stopping due to an error.
  • Example: result <- try(10 / 0) print("Code continues even if an error occurs")

2.2 Using tryCatch()

  • Catches errors and lets you decide what happens next.
  • Example: safe_divide <- function(a, b) { tryCatch({ result <- a / b return(result) }, error = function(e) { print("Error: Cannot divide by zero!") return(NA) }) } safe_divide(10, 0) # Prints error message instead of crashing

2.3 Using stop()

  • Stops execution and displays an error message.
  • Example: check_number <- function(x) { if (!is.numeric(x)) { stop("Input must be a number!") } return(x * 2) } check_number("text") # Stops with an error

2.4 Using warning()

  • Gives a warning but allows the code to continue running.
  • Example: check_age <- function(age) { if (age < 18) { warning("Under 18: Age restriction applies.") } return(age) } check_age(16) # Shows a warning

3. Debugging Tools in R

3.1 Using print() for Debugging

  • Adding print() statements helps track what’s happening.
  • Example: add_numbers <- function(a, b) { print(paste("a is", a)) print(paste("b is", b)) return(a + b) } add_numbers(3, 5)

3.2 Using browser()

  • Stops the code and lets you inspect variables step by step.
  • Example: debug_function <- function(x) { browser() x_squared <- x^2 return(x_squared) } debug_function(4) # Stops execution inside the function

3.3 Using debug()

  • Allows you to step through a function line by line.
  • Example: debug(add_numbers) add_numbers(3, 5) # Now you can step through the function
  • To stop debugging, use: undebug(add_numbers)

3.4 Using traceback()

  • Shows the sequence of function calls that led to an error.
  • Example: faulty_function <- function() { stop("Something went wrong!") } faulty_function() traceback() # Shows where the error occurred

3.5 Using options(error = recover)

  • Opens an interactive mode to explore errors.
  • Example: options(error = recover) faulty_function()
  • After checking, reset to default: options(error = NULL)