Hi I wrote a script which retrieves links from websites and loads them with scan: ... website<-tolower(scan(current.pages[i], what="character", sep="\n", quiet=TRUE)) ... However occasionally, the script finds broken links, such as <http://www.google.com/test>. when the script tries to access such websites, the repeat loop breaks and I get the error message Error in file(file, "r") : unable to open connection In addition: Warning message: cannot open: HTTP status was '404 Not Found' Now my question: is there a way to test whether the target of a link exists that does not result in an error and, thus, discontinues my loop? I looked at the help files for files, scans, connections, and did a search for "404?' in th archives but couldn't find anything. I work with R 2.3.1 patched on Windows XP (both Home and Prof) and would appreciate any pointers ... Thanks a lot, STG
See ?try as in this example:
current.pages <- c("http://www.google.com",
"http://www.google.com/test",
"http://www.yahoo.com")
for(i in seq(along = current.pages)) {
website <- try(tolower(scan(current.pages[i],
what="character", sep="\n", quiet=TRUE)))
if (inherits(website, "try-error")) cat(current.pages[i],
"bad\n")
else cat(current.pages[i], "ok\n")
}
On 9/18/06, Stefan Th. Gries <stgries_lists at arcor.de>
wrote:> Hi
>
> I wrote a script which retrieves links from websites and loads them with
scan:
>
> ...
> website<-tolower(scan(current.pages[i], what="character",
sep="\n", quiet=TRUE))
> ...
>
> However occasionally, the script finds broken links, such as
<http://www.google.com/test>. when the script tries to access such
websites, the repeat loop breaks and I get the error message
>
> Error in file(file, "r") : unable to open connection
> In addition: Warning message:
> cannot open: HTTP status was '404 Not Found'
>
> Now my question: is there a way to test whether the target of a link exists
that does not result in an error and, thus, discontinues my loop? I looked at
the help files for files, scans, connections, and did a search for
"404?' in th archives but couldn't find anything. I work with R
2.3.1 patched on Windows XP (both Home and Prof) and would appreciate any
pointers ...
> Thanks a lot,
> STG
>
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> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
See ?try ?tryCatch On Mon, 18 Sep 2006, Stefan Th. Gries wrote:> Hi > > I wrote a script which retrieves links from websites and loads them with scan: > > ... > website<-tolower(scan(current.pages[i], what="character", sep="\n", quiet=TRUE)) > ... > > However occasionally, the script finds broken links, such as <http://www.google.com/test>. when the script tries to access such websites, the repeat loop breaks and I get the error message > > Error in file(file, "r") : unable to open connection > In addition: Warning message: > cannot open: HTTP status was '404 Not Found' > > Now my question: is there a way to test whether the target of a link exists that does not result in an error and, thus, discontinues my loop? I looked at the help files for files, scans, connections, and did a search for "404?' in th archives but couldn't find anything. I work with R 2.3.1 patched on Windows XP (both Home and Prof) and would appreciate any pointers ... > Thanks a lot, > STG-- Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595