Debugging tools in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print the current call stack.

R Programming

[1]()

Drag options to blanks, or click blank then click option'

Atraceback

Btraceback_print

Attempts:

3 left

💡 Hint

Common Mistakes

Using a function name that does not exist in the traceback package.

Trying to print the call stack without calling the correct function.

The traceback() function prints the current call stack in R, helping you see the sequence of function calls.

2fill in blank

medium

Complete the code to start debugging a function call.

R Programming

debug([1])

Drag options to blanks, or click blank then click option'

Amy_function

Bprint

Csummary

Dplot

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a function call instead of a function name.

Using a built-in function that is not the target for debugging.

The debug() function in R sets a breakpoint on the specified function, here my_function, so you can step through it.

3fill in blank

hard

Fix the error in the code to stop debugging the function.

R Programming

undebug([1])

Drag options to blanks, or click blank then click option'

Amy_function()

Bstop

Cdebug

Dmy_function

Attempts:

3 left

💡 Hint

Common Mistakes

Including parentheses when passing the function name.

Passing a string instead of the function object.

The undebug() function requires the function name without parentheses to stop debugging it.

4fill in blank

hard

Fill both blanks to print the last error message and then clear it.

R Programming

print([1]())
[2]()

Drag options to blanks, or click blank then click option'

Alast_error

Cgeterrmessage

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent function like last_error.

Not calling the function to clear the error message.

geterrmessage() prints the last error message, and calling it again resets the error message in R.

5fill in blank

hard

Fill all three blanks to run code with error handling and print a custom message.

R Programming

tryCatch([1]("a"), error = function(e) {
  print(paste('Error:', [2]))
  [3]()
})

Drag options to blanks, or click blank then click option'

Alog

Be$message

Cstop

Dmean

Attempts:

3 left

💡 Hint

Common Mistakes

Using a function that does not cause errors for demonstration.

Not accessing the error message correctly.

Not stopping execution after printing the error.

tryCatch() runs log("a"). If an error occurs, it prints the error message e$message and then stops execution with stop().

Practice

1. Which R function allows you to step through a function line-by-line to find errors?

easy

A. traceback()

B. debug()

C. browser()

D. stop()

Solution

1. Step 1: Understand the purpose of debug()

   The debug() function lets you step through a function line-by-line to see what happens inside.

2. Step 2: Compare with other functions

   traceback() shows the call stack after an error, browser() pauses execution but debug() is designed for stepping through.

3. Final Answer:

   debug() -> Option B

4. Quick Check:

   Step through function = debug() [OK]

Hint: Use debug() to step through function code line-by-line [OK]

Common Mistakes:

• Confusing traceback() with stepping through code
• Thinking browser() automatically steps through all lines
• Using stop() which just halts execution

2. Which of the following is the correct way to start debugging a function named myFunc in R?

easy

A. debug myFunc()

B. debug:myFunc()

C. debug->myFunc()

D. debug(myFunc)

Solution

1. Step 1: Recall correct debug() syntax

   The debug() function is called with the function name as an argument: debug(myFunc).

2. Step 2: Identify invalid syntax

   Options A, B, and D use invalid R syntax for function calls or operators.

3. Final Answer:

   debug(myFunc) -> Option D

4. Quick Check:

   Correct debug syntax = debug(myFunc) [OK]

Hint: Use parentheses with debug() and function name [OK]

Common Mistakes:

• Omitting parentheses after debug
• Using colon or arrow instead of parentheses
• Adding spaces incorrectly in function call

3. What will be the output after running this R code?

f <- function(x) {
  debug()
  y <- x + 1
  return(y)
}
f(3)

medium

A. Starts debugging mode and waits for user input

B. Returns 4 immediately without debugging

C. Throws an error because debug() needs a function name

D. Prints 3 and exits

Solution

1. Step 1: Understand debug() usage

   debug() is used with a function name outside the function, not inside it.

2. Step 2: Analyze code behavior

   Calling debug() inside a function without arguments causes an error because debug expects a function name.

3. Final Answer:

   Throws an error because debug() needs a function name -> Option C

4. Quick Check:

   debug() inside function without name = error [OK]

Hint: debug() needs a function name, not called inside function body [OK]

Common Mistakes:

• Thinking debug() works inside function without arguments
• Expecting immediate return without debugging
• Confusing debug() with browser()

4. You run a function and get an error. Which R command helps you see the sequence of function calls that led to the error?

medium

A. traceback()

B. debug()

C. browser()

D. stop()

Solution

1. Step 1: Identify purpose of traceback()

   traceback() shows the call stack, listing functions called before the error.

2. Step 2: Differentiate from other tools

   debug() and browser() help step through code, stop() halts execution but does not show call history.

3. Final Answer:

   traceback() -> Option A

4. Quick Check:

   Call stack after error = traceback() [OK]

Hint: Use traceback() to see error call sequence [OK]

Common Mistakes:

• Using debug() to see call stack after error
• Confusing browser() with traceback()
• Expecting stop() to show call history

5. You want to debug a complex function calcStats that calls other functions internally. Which approach helps you pause execution at any line inside calcStats and inspect variables interactively?

hard

A. Use browser() inside calcStats at desired lines

B. Use debug(calcStats) only once before calling

C. Use traceback() after running calcStats

D. Use stop() to halt execution at errors

Solution

1. Step 1: Understand browser() usage

   Inserting browser() pauses execution at that line and lets you inspect variables interactively.

2. Step 2: Compare with debug() and traceback()

   debug() steps through entire function but cannot pause at arbitrary lines; traceback() only shows call stack after error.

3. Step 3: Recognize stop() role

   stop() halts execution with an error but does not allow interactive inspection.

4. Final Answer:

   Use browser() inside calcStats at desired lines -> Option A

5. Quick Check:

   Pause anywhere interactively = browser() [OK]

Hint: Insert browser() where you want to pause and inspect [OK]

Common Mistakes:

• Relying only on debug() to pause anywhere
• Using traceback() before error occurs
• Expecting stop() to allow variable inspection