Error handling (tryCatch)

This lesson covers error handling with R's tryCatch, with the aim of keeping a program running even when something unexpected goes wrong.

tryCatch() catches an error so the whole program does not stop. Think of it as insurance: deciding in advance what to do instead, should something fail.

In the sample code, a divide() function raises an error with stop() on division by zero, and tryCatch({...}, error = function(e) {...}) catches it. Note how conditionMessage(e) pulls the error message out.

A common early stumble is tryCatch's distinctive syntax. It plays the same role as try-catch elsewhere, but writing it as a function — the body in braces, the handler passed as error = function(e) {} — takes some getting used to.

In professional work, tryCatch is used around anything that can fail, such as reading data or talking to an external service.

📖 Reference code

divide <- function(a, b) {
  if (b == 0) stop("cannot divide by zero")
  a / b
}

tryCatch({
  print(divide(10, 2))
  print(divide(10, 0))
}, error = function(e) {
  cat("Error:", conditionMessage(e), "\n")
})

✍️ Your code

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