CODEWITHSUNDEEP
rerror-handlingtry-catch
Bernd Elkemann
Bernd Elkemann

Reputation: 23550

How do you make tryCatch actually catch the error

I have to call a function that throws an error if the arguments didn't satisfy many conditions.

The conditions are so complicated that I cannot try to satisfy them 100% of the time (I would have to re-type all the conditions the function checks internally). Instead, I should just retry calling with different arguments (as many times as necessary to fill my table).

In other languages I can write a catch block around the call.

However, in R tryCatch seems to work differently: you can give code with finally=, but after executing the finally-code the outer function terminates anyway.

Here is a minimal example:

sometimesError <- function() {
    if(runif(1)<0.1) stop("err")
    return(1)
}
fct <- function() {
    theSum <- 0
    while(theSum < 20) {
        tryCatch( theSum <- theSum + sometimesError() )
    }
    return(theSum)
}
fct()    # this should always evaluate to 20, never throw error

( I have read "Is there a way to source() and continue after an error?", and some other posts but I dont think they apply here. They achieve that the source'd code continues statement-by-statement regardless of error as if it were executing at the top level. I, on the other side, am happy with the called function terminating and it is the caller-code that should continue )

Upvotes: 1

Views: 582

Answers (1)

GSee
GSee

Reputation: 49810

You can pass a function to the error argument of tryCatch to specify what should happen when there is an error. In this case, you could just return 0 when there is an error

fct <- function() {
  theSum <- 0
  while(theSum < 20) {
    theSum <- theSum + tryCatch(sometimesError(), error=function(e) 0)
  }
  return(theSum)
}

As @rawr mentioned in the comments, you could also replace tryCatch with try in this case.

fct <- function() {
  theSum <- 0
  while(theSum < 20) {
    try(theSum <- theSum + sometimesError(), silent=TRUE)
  }
  return(theSum)
}

Upvotes: 1

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