implementing tryCatch R - r

Question

Trying to use tryCatch. What I want is to run through a list of urls that I have stored in page1URLs and if there is a problem with one of them (using readHTMLTable() )I want a record of which ones and then I want the code to go on to the next url without crashing.
I think I don't have the right idea here at all. Can anyone suggest how I can do this?
Here is the beginning of the code:
baddy <- rep(NA,10,000)
badURLs <- function(url) { baddy=c(baddy,url) }
writeURLsToCsvExtrema(38.361042, 35.465144, 141.410522, 139.564819)
writeURLsToCsvExtrema <- function(maxlat, minlat, maxlong, minlong) {
urlsFuku <- page1URLs
allFuku <- data.frame() # need to initialize it with column names
for (url in urlsFuku) {
tryCatch(temp.tables=readHTMLTable(url), finally=badURLs(url))
temp.df <- temp.tables[[3]]
lastrow <- nrow(temp.df)
temp.df <- temp.df[-c(lastrow-1,lastrow),]
}

Answer 1

One general approach is to write a function that fully processes one URL, returning either the computed value or NULL to indicate failure
FUN = function(url) {
tryCatch({
xx <- readHTMLTable(url) ## will sometimes fail, invoking 'error' below
## more calculations
xx ## final value
}, error=function(err) {
## what to do on error? could return conditionMessage(err) or other...
NULL
})
}
and then use this, e.g., with a named vector
urls <- c("http://cran.r-project.org", "http://stackoverflow.com",
"http://foo.bar")
names(urls) <- urls # add names to urls, so 'result' elements are named
result <- lapply(urls, FUN)
These guys failed (returned NULL)
> names(result)[sapply(result, is.null)]
[1] "http://foo.bar"
And these are the results for further processing
final <- Filter(Negate(is.null), result)