R help - Oct 2007 - try / tryCatch for download.file( ) within a for loop when URL does not exist

I am trying to download a bunch of files from a server, for which I am
using download.file( ) within a for loop. The script is working fine
except until download.file hits a URL which has no file, at which
point it exits. I want to change this behavior to simple log the
failure and maintain state within the for loop and iterate to next. I
read about try / tryCatch but am having trouble understanding what/how
it does. Thanks.

#begin script

date <- as.POSIXlt(as.Date("2007-10-15", "%Y-%m-%d"))
for (i in 1:difftime(as.POSIXlt(as.Date("2007-10-15",
"%Y-%m-%d")),"2007-10-01"))
	{
	if (date$wday != 0 & date$wday != 6) {
	datestr <- as.character(date, "%d%m%y") #make date character
string ddmmyy
	url <-
paste("http://www.bseindia.com/bhavcopy/eq",datestr,"_csv.zip",sep="")
	file <- paste("C:/",datestr,"_csv.zip",sep="")
	#options(show.error.messages = FALSE)
	#options(warn = -1)
	try(download.file(url, destfile = file, quiet = TRUE, mode = "wb"),
finally = cat("OK:",url,\n))
	date <- as.POSIXlt(as.Date(date - 86400))
	} else {date <- as.POSIXlt(as.Date(date - 86400))}
	}

# end script


Thanks,

Vishal Belsare

I think this is closer to what you want. You can determine what you
want to do; this one just goes to the next iteration:


date <- as.POSIXlt(as.Date("2007-10-15", "%Y-%m-%d"))
for (i in 1:difftime(as.POSIXlt(as.Date("2007-10-15",
"%Y-%m-%d")),"2007-10-01"))
       {
       if (date$wday != 0 & date$wday != 6) {
       datestr <- as.character(date, "%d%m%y") #make date character
string ddmmyy
       url <-
paste("http://www.bseindia.com/bhavcopy/eq",datestr,"_csv.zip",sep="")
       file <-
paste("C:/",datestr,"_csv.zip",sep="")
       #options(show.error.messages = FALSE)
       #options(warn = -1)
       err <- try(download.file(url, destfile = file, quiet = TRUE,
mode = "wb"))
       if (class(err) == "try-error") next  # skip this iteration on
error
       date <- as.POSIXlt(as.Date(date - 86400))
       } else {date <- as.POSIXlt(as.Date(date - 86400))}
       }



On 10/16/07, Vishal Belsare <shoot.spam at gmail.com>
wrote:
> I am trying to download a bunch of files from a server, for which I am
> using download.file( ) within a for loop. The script is working fine
> except until download.file hits a URL which has no file, at which
> point it exits. I want to change this behavior to simple log the
> failure and maintain state within the for loop and iterate to next. I
> read about try / tryCatch but am having trouble understanding what/how
> it does. Thanks.
>
> #begin script
>
> date <- as.POSIXlt(as.Date("2007-10-15",
"%Y-%m-%d"))
> for (i in 1:difftime(as.POSIXlt(as.Date("2007-10-15",
> "%Y-%m-%d")),"2007-10-01"))
>        {
>        if (date$wday != 0 & date$wday != 6) {
>        datestr <- as.character(date, "%d%m%y") #make date
character string ddmmyy
>        url <-
paste("http://www.bseindia.com/bhavcopy/eq",datestr,"_csv.zip",sep="")
>        file <-
paste("C:/",datestr,"_csv.zip",sep="")
>        #options(show.error.messages = FALSE)
>        #options(warn = -1)
>        try(download.file(url, destfile = file, quiet = TRUE, mode =
"wb"),
> finally = cat("OK:",url,\n))
>        date <- as.POSIXlt(as.Date(date - 86400))
>        } else {date <- as.POSIXlt(as.Date(date - 86400))}
>        }
>
> # end script
>
>
> Thanks,
>
> Vishal Belsare
>
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>

-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?