On Mon, 11 May 2009, Dennis Fisher wrote:
Colleagues,
I have encountered a problem in version 2.9 of R, running in both Vista and
OS X. My code is quite lengthy but the critical line is:
if (file.exists(FILENAME)) readLines(FILENAME))
This triggers the error:
Error in file(con, "r") : cannot open the connection
Calls: readLines -> file
Execution halted
The file that it is reading is being created on the fly, then eventually
deleted. The conditional was used to ensure that the readLines command would
be executed only when the file existed.
Is it possible that the file is deleted AFTER the conditional is evaluated
but before the readLines command is executed? If so, is there any means to
prevent an error condition?
It is possible. But so are a lot of other things, and your pretest is
just not enough -- for example another process might have the file
open for exclusive access (quite common in the Windows world) in which
case it exists but you cannot open it for reading.
There is only one sure way to find out if you can read a file, and
that is to try to read it. So I'd simply use try() or tryCatch() on
the readLines call.
Any help will be greatly appreciated. Thanks.
Dennis
Dennis Fisher MD
P < (The "P Less Than" Company)
Phone: 1-866-PLessThan (1-866-753-7784)
Fax: 1-415-564-2220
www.PLessThan.com
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--
Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
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