[R] download.file error

From: CHIB CO <chibco_at_hotmail.com>
Date: Tue, 01 Apr 2008 00:26:25 +0100

Dear all,

I am looking for a way to work out if a file on the internet exists before attempting to download it using the function download.file(). For example, using a url that does not exist

url <- "http://finance.yahoo.com/ftse.csv" destfile <- tempfile()
download.file(url = url, destfile = destfile)

# gives the following response ...

trying URL 'http://finance.yahoo.com/ftse.csv' Error in download.file(url = url, destfile = destfile) :   cannot open URL 'http://finance.yahoo.com/ftse.csv' In addition: Warning message:
In download.file(url = url, destfile = destfile) :   cannot open: HTTP status was '404 Not Found'

When I am using the download.file() function in a loop over multiple URLs, the above error will cause the loop to terminate, so I want to avoid this by checking if the file exists first then wrapping the subsequent functions in an if() statment. The original fault came from the function get.hist.quote() in the "tseries" package. I was trying to iterate over various stocks, but some stocks listed in the yahoo website do not have any downloadable data associated with them, which causes the loop to terminate. The "workhorse" function of get.hist.quote() is the download.file() function.

Kind Regards

Chib



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