R help - Nov 2010 - how to know if a file exists on a remote server?

Hi,

I'd like to download some data files from a remote server, the problem
here is that some of the files actually don't exist, which I don't
know before try. Just wondering if a function in R could tell me if a
file exists on a remote server? I searched this mailing list and after
read severals mails, still clueless.  Any help will be highly
appreciated.

B.C.

Take a look on ?file_test

On Tue, Nov 30, 2010 at 2:10 PM, Baoqiang Cao <bqcaomail@gmail.com> wrote:
> Hi,
>
> I'd like to download some data files from a remote server, the problem
> here is that some of the files actually don't exist, which I don't
> know before try. Just wondering if a function in R could tell me if a
> file exists on a remote server? I searched this mailing list and after
> read severals mails, still clueless.  Any help will be highly
> appreciated.
>
> B.C.
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

	[[alternative HTML version deleted]]

?file.exists

On Tue, Nov 30, 2010 at 11:10 AM, Baoqiang Cao <bqcaomail at gmail.com>
wrote:
> Hi,
>
> I'd like to download some data files from a remote server, the problem
> here is that some of the files actually don't exist, which I don't
> know before try. Just wondering if a function in R could tell me if a
> file exists on a remote server? I searched this mailing list and after
> read severals mails, still clueless. ?Any help will be highly
> appreciated.
>
> B.C.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


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

What is the problem that you are trying to solve?

I would use RCurl.

 if you have, for example, the url of an ftp site you can merely do a
getURL() and the contents will be returned. That call will return data that
can be coerced into a data.frame that will look like a directory structure
listing the file names.

If you need code just ask, but the RCurl docs are pretty good.



On Tue, Nov 30, 2010 at 8:10 AM, Baoqiang Cao <bqcaomail@gmail.com> wrote:
> Hi,
>
> I'd like to download some data files from a remote server, the problem
> here is that some of the files actually don't exist, which I don't
> know before try. Just wondering if a function in R could tell me if a
> file exists on a remote server? I searched this mailing list and after
> read severals mails, still clueless.  Any help will be highly
> appreciated.
>
> B.C.
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
	[[alternative HTML version deleted]]

using RCurl

getFtpList <- function(ftp){

    # the structure returned is dependent on the ftp site as there are
    # various formats for directory listings dependent upon the server
    # and the OS. you will need to play with this.
    # have a look at the ftp with your browser first and adjust accordingly.
    # some formats only return 4 columns.
    # column 1= literal string first position mean file
    # column 2= number 1
    # column 3 =owner
    # column 4 = group
    # column 5 =file size
    # colmn  6 =Month
    # column 7 =Day
    # column 8 =Time (year)
    # column 9 =FileName
    #
    txt <- getURL(ftp)

    dir <- read.table( textConnection(txt),as.is=TRUE)
    out <- data.frame(Dir=ftp,Filename=dir[, ncol(dir)],Size=dir[ ,5],
                      Month=dir[ ,6],Day=dir[ ,7],Time=dir[
,8],stringsAsFactors=FALSE)
    closeAllConnections()
    return(out)
}

On Tue, Nov 30, 2010 at 8:10 AM, Baoqiang Cao <bqcaomail@gmail.com> wrote:
> Hi,
>
> I'd like to download some data files from a remote server, the problem
> here is that some of the files actually don't exist, which I don't
> know before try. Just wondering if a function in R could tell me if a
> file exists on a remote server? I searched this mailing list and after
> read severals mails, still clueless.  Any help will be highly
> appreciated.
>
> B.C.
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
	[[alternative HTML version deleted]]

On 30/11/10 10:10:07, Baoqiang Cao wrote:
> I'd like to download some data files from a remote server, the problem
> here is that some of the files actually don't exist, which I don't
> know before try. Just wondering if a function in R could tell me if a
> file exists on a remote server? 
Hi Baoqiang,

try downloading the file with R's download.file() function. Then you
should examine the returned value.

Citing a part of ?download.file below:
>> Value:
>> An (invisible) integer code, ?0? for success and non-zero for
>> failure.  For the ?"wget"? and ?"lynx"? methods
this is the status
>> code returned by the external program.  The ?"internal"?
method can
>> return ?1?, but will in most cases throw an error.
So if you call your download via 

v <- download.file(url, destfile, method="wget") 

and v is not equal to zero, then the file is likely to be non-existent (at
least the download failed). Note: the method "internal" doesn't
really
change the value of v, I just tried that. With "wget" it returns
"0" for
success and "2048" (or some other value) for non-success.

Regards,
Georg.
-- 
Research Assistant
Otto-von-Guericke-Universit?t Magdeburg
research at georgruss.de
http://research.georgruss.de