Re: [R] Zipping Rdata Files

From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>
Date: Fri 08 Apr 2005 - 16:33:34 EST

On Thu, 7 Apr 2005 Brian.J.GREGOR@odot.state.or.us wrote:

> Saving Rdata files in a zip archive form can in some cases save a
> considerable amount of disk space.

Not if they were saved with compress=TRUE: it is likely to increase the size of compressed saved images.

> R has the zip.file.extract function to extract files from zip archives,
> but appears not to have any corresponding function to save in zipped
> form. (At least I have not been able to find anything in the help files
> or through searching the mail archives.)

That is true, but I think you are looking for gzip format. If you want zip format, just use a system call to zip (if you have it). zip.file.extract is provided only because R for Windows needs to unzip on systems without unzip. (On other platforms it calls unzip.)

> The system function can be used to call gzip or some other utility, but
> perhaps there is a more direct method.

Yes, for gzip (not zip). gzfile() connections, as used by save(compress=TRUE) and by load().

> Also, when I use gzip to zip a file, I get an error message when using

That's because gzip >g<zips a file, not zips a file. gzip and zip are different formats.

> zip.file.extract to extract the file as follows:
> > save(trips, file="trips.Rdata")
> > system("gzip trips.Rdata") # saves trips.Rdata in an archive
> named trips.Rdata.gz
> > load(zip.file.extract("trips.Rdata", "trips.Rdata.gz"))
> [1] "trips.Rdata"
> Warning message:
> error 1 in extracting from zip file
> Setting options(unzip="gunzip") or options(unzip="gunzip.exe") does not
> solve the error.
> > load(zip.file.extract("trips.Rdata", "trips.Rdata.gz"))
> Error in open.connection(con, "rb") : unable to open connection
> In addition: Warning message:
> cannot open compressed file `trips.Rdata'
>
> Of course I could reverse the process with,
> system("gunzip trips.Rdata.gz")
> load("trips.Rdata")
> but perhaps there is a simpler solution.
>
> P.S. I'm running R 2.0.1 on a Windows XP computer.

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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Received on Fri Apr 08 16:41:25 2005

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