Debugging tools in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of debugged function with browser()

Consider the following R function that uses browser() for debugging. What will be the output when calling sum_squares(3)?

R Programming

sum_squares <- function(n) {
  browser()
  total <- 0
  for (i in 1:n) {
    total <- total + i^2
  }
  return(total)
}
sum_squares(3)

A [1] 14

B [1] 6

C Error in sum_squares(3) : object 'total' not found

D [1] 9

💡 Hint

Remember that the function sums squares of numbers from 1 to n.

The function sums 1^2 + 2^2 + 3^2 = 1 + 4 + 9 = 14. The browser() pauses execution but does not change the output.

❓ Predict Output

intermediate

Effect of traceback() after error

What will be the output of the following R code snippet?

R Programming

f <- function(x) {
  g(x)
}
g <- function(y) {
  stop("Error occurred")
}
tryCatch(f(5), error = function(e) {traceback(); print("Handled error")})

A No output, program stops

B Error in g(x) : Error occurred

C

1: stop("Error occurred")
[1] "Handled error"

D

3: g(x)
2: f(5)
[1] "Handled error"

💡 Hint

traceback() shows the call stack at the error point.

traceback() prints the call stack showing g called by f, then the error handler prints "Handled error".

❓ Predict Output

advanced

Output of debug() with step-through

Given the code below, what will be printed when debugged_sum(2) is called and the user steps through the function until it returns?

R Programming

debugged_sum <- function(n) {
  debug()
  s <- 0
  for (i in 1:n) {
    s <- s + i
  }
  return(s)
}
debugged_sum(2)

A [1] 3

B [1] 2

C Error: debug() requires a function argument

D [1] 0

💡 Hint

Check how debug() is used in R.

debug() must be called with a function name as argument, calling debug() inside a function without argument causes an error.

❓ Predict Output

advanced

Behavior of options(error = recover)

What happens when you run the following code and an error occurs?

R Programming

options(error = recover)
f <- function(x) {
  g(x)
}
g <- function(y) {
  stop("Oops")
}
f(1)

A No output, silently fails

B Interactive menu to choose a frame to debug

C Program stops with error message 'Oops'

D Prints traceback and continues execution

💡 Hint

options(error = recover) triggers a debugging menu on error.

When an error occurs, recover() lets you select which function frame to inspect interactively.

🧠 Conceptual

expert

Identifying the cause of silent failure in R script

You run an R script that uses try() to catch errors but notice that some errors do not appear and the script continues silently. Which of the following best explains this behavior?

A <code>try()</code> suppresses errors and returns an object of class 'try-error' without stopping execution

B <code>try()</code> always stops execution on error and prints the error message

C <code>try()</code> converts errors into warnings that are printed immediately

D <code>try()</code> logs errors to a file but does not affect console output

💡 Hint

Think about how try() handles errors differently than stop().

try() catches errors and returns an object indicating failure but does not stop the script, so errors may be silent unless checked.