R help - Nov 2010 - ff objects saving problem

Hi,
	I am running the examples in page 70 of the ff package document, but it failed
with the following error
> cat("let's create some ff objects\n")
let's create some ff objects
> n <- 8e3
> a <- ff(sample(n, n, TRUE), vmode="integer", length=n,
filename="d:/tmp/a.ff")
> b <- ff(sample(255, n, TRUE), vmode="ubyte", length=n,
filename="d:/tmp/b.ff")
> x <- ff(sample(255, n, TRUE), vmode="ubyte", length=n,
filename="d:/tmp/x.ff")
> y <- ff(sample(255, n, TRUE), vmode="ubyte", length=n,
filename="d:/tmp/y.ff")
> z <- ff(sample(255, n, TRUE), vmode="ubyte", length=n,
filename="d:/tmp/z.ff")
> df <- ffdf(x=x, y=y, z=z)
> rm(x,y,z)
> cat("save some of them with shorter relative pathnames ...\n")
save some of them with shorter relative pathnames ...
> ffsave(a, b, file="d:/tmp/y", rootpath="d:/tmp")
Error in system(cmd, input = list, intern = TRUE) : 'zip' not
found
> str(ffinfo("d:/tmp/y"))
Error in system(cmd, intern = TRUE) : 'unzip' not found

Does it mean I have to install some special softwares for zip and unzip
operation.


Another question is whether ff always create physical files for vectors, I found
when a ff ffdf object is created, the number of physical files created is eaqual
to the number of data frame columns.


Xiaobo.Gu

Xiaobo,

You indeed need external 'zip' and 'unzip' utlities in the path,
citing from ffsave's help: "using an external zip utility, e.g. for
windows in Rtools on [http://www.murdoch-sutherland.com/Rtools/]".

Please note that the mentioned utilities have a 4 GB limit for the zip file,
AFAIK. I will for the next release check for a way to get rid of this limit and
also to get rid of inconsistencies in upper/lower-case spelling of drive letters
which can cause ffsave to fail. Note that - even without fffsave - ff objects
can be made permanent simply by creating them with 'filename' resp.
'pattern' outside of fftempdir and saving the R-side ff-object with the
usual 'save' or 'save.image' function.

In a new R session, after 'library(ff)' and 'load' you again
have access, assumed your ff files are still in the same location.
And yes, each column of a ffdf dataframe is stored as a separate ff file. 

Jens Oehlschl?gel