Using tryCatch and source

Question

Suppose I have two R files: correct.R and broken.R. What would be the best way of using tryCatch to check for errors?

Currently, I have

> x = tryCatch(source("broken.R"), error=function(e) e)
> x
 <simpleError in source("broken.R"): test.R:2:0: unexpected end of input
  1: x = {
     ^>
> y = tryCatch(source("correct.R"), error=function(e) e)
> y
 $value
 [1] 5

 $visible
 [1] FALSE

However, the way I've constructed the tryCatch means that I have to interrogate the x and y objects to determine if there has been an error.

Is there a better way of doing this?

The question comes from teaching. 100 students upload their R scripts and I run the scripts. To be nice, I'm planning on creating a simple function that determines if their function sources correctly. It only needs to return TRUE or FALSE.

Note that tryCatch will report only the first error it bumps onto. — aL3xa
– aL3xa, Commented Mar 7, 2011 at 21:32

Richie Cotton · Accepted Answer · 2011-03-07 14:12:52Z

6

To expand upon mdsumner's point, this is a simple implementation.

sources_correctly <- function(file)
{
  fn <- try(source(file))
  !inherits((fn, "try-error"))
}

answered Mar 7, 2011 at 14:12

Richie Cotton

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Comments

aL3xa · Accepted Answer · 2011-03-07 12:03:23Z

4

Try this:

> tryCatch(stop("foo"), error = function(e) {
+ cat(e$message, "\n")
+ FALSE
+ })
foo 
[1] FALSE

Alternatively, you should consider Hadley's testthat package:

> expect_that(stop("foo"), is_a("numeric"))
Error in is.vector(X) : foo

answered Mar 7, 2011 at 12:03

aL3xa

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Comments

Noah · Accepted Answer · 2011-03-07 11:53:19Z

3

Maybe I'm underthinking this, but since you're just looking for the boolean, you can just test for the existence of the $visible:

y <- tryCatch(source("broken.R"), error=function(e) e)
works <- !is.null(y$visible) #y$visible would be null if there were an error

Does that solve what you're looking for? You could wrap it in a loop (or use lapply) like:

for(i in 1:length(students)) {
  works[i] <- !is.null(tryCatch(source(student_submissions[i]), error=function(e) e)$visible)
}

answered Mar 7, 2011 at 11:53

Noah

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2 Comments

csgillespie Over a year ago

That's what I'm doing, it just seemed clunky. I suppose I was looking for an is.error command.

mdsumner Over a year ago

er, with objects from try that is, not tryCatch

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