>>>>> "RT" == Rolf Turner <[EMAIL PROTECTED]>
>>>>> on Wed, 14 May 2008 13:12:02 +1200 writes:
RT> I have written a function which reads data from files using read.delim
RT> ().
RT> The names of these files are complicated and are built using arguments
RT> to the wrapper function. Since the files in question may or may not
RT> exist, I thought to enclose the read.delim() call in a try():
RT> file <- <complicated expression>
RT> temp <- try(read.delim(file))
RT> if(inherits(temp,"try-error")) {
RT> (Do something)
RT> } else {
RT> (Do something else)
RT> }
RT> But this doesn't work. If file doesn't exist, then I get an error,
You get an error *message* but not an error, I'd think.
If you don't like the error *message* in this case, use
try(..., silent=TRUE)
In R, try() is now using tryCatch(), (type 'try' to see)
and I would nowadays recommend using tryCatch() inside any function.
Another "advantage" of tryCatch(.) for you is that you can
decide yourself what to do with the error message.
The most simple thing would be something like
if(is.null(tryCatch(temp <- read.delim(file),
error = function(e) NULL))) {
## error reading ...
} else {
## work with the 'temp' data frame
}
Slightly more sophisticated
temp <- tryCatch(read.delim(file), error = function(e) e)
if(inherits(e, "error") {
message("Caught error:", [EMAIL PROTECTED], "\n")
## error reading ...
} else {
## work with the 'temp' data frame
}
*However*, there's a small infelicity in the above:
You get an additional warning from file(..) which you need to
suppress by another suppressWarnings( ..... )
around the call.
Martin
RT> and the wrapper function terminates, despite the presence of the try().
RT> The object ``temp'' never gets created.
RT> I can of course easily get around the problem by testing with
RT> file.exists(file)
RT> I just wondered --- why isn't try() working as expected here? Am I
RT> being
RT> silly to expect it to work? If so, what am I not understanding about
RT> try()?
RT> Thanks for any insights.
RT> cheers,
RT> Rolf
RT> ######################################################################
RT> Attention:\ This e-mail message is privileged and confid...{{dropped:9}}
RT> ______________________________________________
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RT> https://stat.ethz.ch/mailman/listinfo/r-help
RT> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
RT> and provide commented, minimal, self-contained, reproducible code.
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