[R] check for new files in a given directory

[Martin Maechler]

>>>>> William Dunlap <wdunlap at tibco.com>
>>>>>     on Tue, 28 Jul 2009 08:50:29 -0700 writes:

    >> -----Original Message-----
    >> From: r-help-bounces at r-project.org 
    >> [mailto:r-help-bounces at r-project.org] On Behalf Of Barry Rowlingson
    >> Sent: Tuesday, July 28, 2009 6:41 AM
    >> To: ted.harding at manchester.ac.uk
    >> Cc: r-help at r-project.org; Andreas Posch
    >> Subject: Re: [R] check for new files in a given directory
    >> 
    >> On Tue, Jul 28, 2009 at 12:36 PM, Ted
    >> Harding<Ted.Harding at manchester.ac.uk> wrote:
    >> 
    >> > However, this got me looking into '?list.files, and I see there
    >> > (R version 2.9.0 (2009-04-17)):
    >> >
    >> >  recursive: logical. Should the listing recurse into directories?
    >> >
    >> > But:
    >> >
    >> >  Directories are included only if 'recursive = FALSE'.
    >> >
    >> > Surely the latter is the wrong way round, and should be
    >> >
    >> >  Directories are included only if 'recursive = TRUE'.
    >> >
    >> 
    >> by 'included' it means 'returned'. If you do 'recursive=TRUE' it
    >> scans recursively for files and only files. If you do
    >> "recursive=FALSE" it returns files and directories in the specified
    >> directory.
    >> 
    >> Makes it tricky to figure out a complete directory tree since empty
    >> directories won't appear at all if recursive=TRUE. You'd have to
    >> implement your own recursive search based on
    >> list.files(d,recursive=FALSE) and then testing for directoriness....
    >> 
    >> Sucky, unless there's a better way...
    >> 
    >> Barry

    > S+'s dir() and list.files() functions have an extra argument called "type"
    > that let you say if you are interested in only "files" (non-directories) or
    > directories or want all directory entries listed in the
    > output.  Its default value is set to match the R behavior

    > function(...,
    > recursive=FALSE,
    > type = if(recursive) c("files", "directories", "all") else c("all", "files", "directories"))
    > {
    > type <- match.arg(type)
    > ...
    > }

    > I put it in when I was looking for all directories named 'R' in a collection of
    > packages and bundles and I didn't want to use the platform-dependent
    > system() function.  Should this argument be added to R's dir() and
    > list.files() functions?

Yes, I think it "should" -- exactly because I also like to work
without system() here.
I will not implement it myself though, as I nowadays build R
only for Linux {or intermittently, one flavor of Solaris},
and from recent "experience" with file.access() {not working 
reliably on some Windows-version x file-system combination},
this doesn't seem easy to get right.
I think R core would be very grateful for patches (particularly
if from someone as qualfied as you).

Martin Maechler, ETH Zurich

    > Bill Dunlap
    > TIBCO Software Inc - Spotfire Division
    > wdunlap tibco.com