R help - Mar 2010 - capturing errors in Sweave

Hi,

I'm writing a manual using Sweave and I want to be able to print errors from
bad code. Here's an example:

<Function-4a>>MySqrt <- function(x) {
  if (missing(x)) {
    stop("'x' is missing with no default")
  }
  if (!is.numeric(x)) {
    stop("'x' should only be numeric")
  }
  if (x < 0) {
    stop("'x' should be non-negative")
  }
  return(sqrt(x))
}
MySqrt()
MySqrt("a")
MySqrt(-2)
MySqrt(4)
@

And I would like the output to be:

MySqrt <- function(x) {
...
}
> MySqrt()
Error in MySqrt() : 'x' is missing with no
default
> MySqrt("a")
Error in MySqrt("a") : 'x' should only be
numeric
> MySqrt(-2)
Error in MySqrt(-2) : 'x' should be non-negative
> MySqrt(2)
[1] 1.414214

I.e. I want the Error statements to print in the tex file and not just make
Sweave to bomb.

Thanks,

--sundar

	[[alternative HTML version deleted]]

Sundar Dorai-Raj-2 wrote:
> 
> Hi,
> 
> I'm writing a manual using Sweave and I want to be able to print errors
> from
> bad code. Here's an example:
> 
> <Function-4a>>> MySqrt <- function(x) {
>   if (missing(x)) {
>     stop("'x' is missing with no default")
>   }
>   if (!is.numeric(x)) {
>     stop("'x' should only be numeric")
>   }
>   if (x < 0) {
>     stop("'x' should be non-negative")
>   }
>   return(sqrt(x))
> }
> MySqrt()
> MySqrt("a")
> MySqrt(-2)
> MySqrt(4)
> @
> 
> And I would like the output to be:
> 
> MySqrt <- function(x) {
> ...
> }
>> MySqrt()
> Error in MySqrt() : 'x' is missing with no default
>> MySqrt("a")
> Error in MySqrt("a") : 'x' should only be numeric
>> MySqrt(-2)
> Error in MySqrt(-2) : 'x' should be non-negative
>> MySqrt(2)
> [1] 1.414214
> 
> I.e. I want the Error statements to print in the tex file and not just
> make
> Sweave to bomb.
> 
> Thanks,
> 
> --sundar
> 
You can catch errors in R using the try() function:

  foo <- try( log("A"), silent = TRUE )

  if( class( foo ) == 'try-error' ){

    print( unclass( foo ) )

  }

[1] "Error in log(\"A\") : Non-numeric argument to mathematical
function\n"


There might be a more clever way to override the default error handling that
would save you from wrapping everything in try()-- but this method should
work.

Hope it helps!

-Charlie

-----
Charlie Sharpsteen
Undergraduate-- Environmental Resources Engineering
Humboldt State University
-- 
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