Error handling (tryCatch) in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this tryCatch example?

Consider the following R code using tryCatch. What will be printed when it runs?

R Programming

result <- tryCatch({
  stop("Error happened")
  10
}, error = function(e) {
  "Caught error"
})
print(result)

A [1] 10

B NULL

C Error in stop("Error happened"): Error happened

D [1] "Caught error"

💡 Hint

Remember that stop() causes an error and tryCatch handles it.

The stop() function triggers an error, so the error handler runs and returns "Caught error". The print shows this string.

❓ Predict Output

intermediate

What does this tryCatch return when no error occurs?

Look at this R code. What is the value of 'result' after running?

R Programming

result <- tryCatch({
  5 + 3
}, error = function(e) {
  0
})
print(result)

A Error in 5 + 3 : non-numeric argument to binary operator

B [1] 0

C [1] 8

D NULL

💡 Hint

No error is triggered in the expression 5 + 3.

Since 5 + 3 runs without error, tryCatch returns 8 directly.

❓ Predict Output

advanced

What error does this code raise?

What error message will this R code produce?

R Programming

tryCatch({
  log("a")
}, error = function(e) {
  stop("Custom error")
})

A Error: Custom error

B Warning message: In log("a") : NaNs produced

C NULL

D Error in log("a"): non-numeric argument to mathematical function

💡 Hint

The error handler re-throws a new error with stop().

The original error is caught, but the handler calls stop() with "Custom error", so that error is raised.

🧠 Conceptual

advanced

Which option correctly catches warnings with tryCatch?

You want to catch warnings in R using tryCatch. Which code snippet correctly catches a warning?

A tryCatch({ warning("Watch out!") }, warning = function(w) { print("Warning caught") })

B tryCatch({ warning("Watch out!") }, error = function(e) { print("Warning caught") })

C tryCatch({ warning("Watch out!") }, finally = function(f) { print("Warning caught") })

D tryCatch({ warning("Watch out!") }, message = function(m) { print("Warning caught") })

💡 Hint

Use the 'warning' argument to catch warnings.

The warning argument in tryCatch handles warnings. Others like error or message do not catch warnings.

🔧 Debug

expert

Why does this tryCatch not catch the error?

This R code does not catch the error as expected. What is the reason?

R Programming

tryCatch({
  stop("Fail")
}, warning = function(w) {
  print("Warning caught")
})

A stop() does not generate an error, so tryCatch does nothing.

B The error handler is missing; only warning handler is defined, so error is not caught.

C The warning handler catches errors too, so this should work.

D tryCatch requires a finally block to catch errors.

💡 Hint

stop() triggers an error, not a warning.

tryCatch only catches errors if an error handler is provided. Here only warning handler is given, so error is not caught and stops execution.