Thanks very much Milan.  Your answer makes perfect sense.

Best,

Andrew


On Wed, Feb 13, 2013 at 3:51 AM, Milan Bouchet-Valat <nalimilan@club.fr>wrote:

> Le mardi 12 février 2013 à 15:41 -0600, Andrew Barr a écrit :
> > Hi all,
> >
> > I am searching for a way to recover results from lapply() when one or
> more
> > values returns an error.  I have a written a function that uses
> tryCatch()
> > to recover from errors. Here is a very simple example of such a function.
> >
> > divideBy2<-function(X){
> >   result<-tryCatch(X/2, error = function(e) "An Error Occurred")
> >   return(result)
> > }
> >
> > This function appears to work as I expect both in cases where an error
> > occurs and where no error occurs.
> >
> > divideBy2(10)
> > # [1] 5
> >
> > divideBy2("This is not a number")
> > # [1] "An Error Occurred"
> >
> > I would like to use this function in an lapply(), but when I do so ALL of
> > the results returned are the results of an error.
> >
> > lapply(c(10,"This is not a number"),FUN=divideBy2)
> >
> > #[[1]]
> > #[1] "An Error Occurred"
> >
> > #[[2]]
> > #[1] "An Error Occurred"
> >
> > Is this how lapply() is meant to work? What I want is a list that looks
> > like this
> The problem happens before lapply() itself:
> > c(10,"This is not a number")
> [1] "10"  "This is not a number"
>
> A vector can only contain values of the same type, so 10 is converted to
> a character value, and divideBy2("10") does not work. Try with:
> lapply(list(10, "This is not a number"), divideBy2)
>
> All that means that in real use cases, your tryCatch() solution should
> work (I have not tested it). The bug is in your toy example.
>
>
> Regards
>
> > #[[1]]
> > #[1] 5
> > #[[2]]
> > #[1] "An Error Occurred"
> >
> > Thanks very much for your time.
> >
> >       [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
>
>

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