ffsave: Save R and ff objects
In kindlychung/ff: memory-efficient storage of large data on disk and fast access functions

Description Usage Arguments Details Value Note Author(s) See Also Examples

ffsave writes an external representation of R and ff objects to an ffarchive. The objects can be read back from the file at a later date by using the function ffload.

ffsave(...
, list = character(0L)
, file = stop("'file' must be specified")
, envir = parent.frame()
, rootpath = NULL
, add = FALSE

, move = FALSE
, compress = !move
, compression_level = 6
, precheck=TRUE
)
ffsave.image(file = stop("'file' must be specified"), safe = TRUE, ...)

`...`	For `ffsave` the names of the objects to be saved (as symbols or character strings), for `ffsave.image` further arguments passed to `ffsave`
`list`	A character vector containing the names of objects to be saved.
`file`	A name for the the `ffarchive`, i.e. the two files `<file>.RData` and `<file>.ffData`
`envir`	environment to search for objects to be saved.
`add`	logical indicating whether the objects shall be added to the `ffarchive` (in this case `rootpath` is taken from an existing archive)

`move`	logical indicating whether ff files shall be moved instead of copied into the `<file>.ffData`
`compress`	logical specifying whether saving to a named file is to use compression.
`compression_level`	compression level passed to `zip`, default 6
`rootpath`	optional path component that all all ff files share and that can be dropped/replaced when calling `ffload`
`precheck`	logical: should the existence of the objects be checked before starting to save (and in particular before opening the file/connection)?
`safe`	logical. If `TRUE`, a temporary file is used for creating the saved workspace. The temporary file is renamed to `<file>.ffData` if the save succeeds. This preserves an existing workspace `<file>.ffData` if the save fails, but at the cost of using extra disk space during the save.

ffsave stores objects and ff files in an ffarchive named <file>: i.e. it saves all specified objects via save in a file named <file>.RData and saves all ff files related to these objects in a zipfile named <file>.ffData using an external zip utility.
By default files are stored relative to the rootpath="\"} and will be restored relative to \code{"\" (in its original location). By providing a partial path prefix via argument rootpath the files are stored relative to this rootpath. The rootpath is stored in the <file>.RData with the name .ff.rootpath. I.e. even if the ff objects were saved with argument rootpath to ffsave, ffload by default restores in the original location. By using argument rootpath to ffload you can restore relative to a different rootpath (and using argument rootpath to ffsave gave you shorter relative paths)
By using argument add in ffsave you can add more objects to an existing ffarchive and by using argument list in ffload you can selectively restore objects.
The content of the ffarchive can be inspected using ffinfo before actually loading any of the objects.
The ffarchive can be deleted from disk using ffdrop.

a character vector with messages returned from the zip utility (one for each ff file zipped)

The ff files are not platform-independent with regard to byte order. For large files and the zip64 format use zip 3.0 and unzip 6.0 from http://www.info-zip.org/.

Jens Oehlschl<c3><a4>gel

ffinfo for inspecting the content of the ffarchive
ffload for loading all or some of the ffarchive
ffdrop for deleting one or more ffarchives

  ## Not run: 
  message("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)

  message("save all of them")
  ffsave.image("d:/tmp/x")
  str(ffinfo("d:/tmp/x"))

  message("save some of them with shorter relative pathnames ...")
  ffsave(a, b, file="d:/tmp/y", rootpath="d:/tmp")
  str(ffinfo("d:/tmp/y"))

  message("... and add others later")
  ffsave(df, add=TRUE, file="d:/tmp/y", rootpath="d:/tmp")
  str(ffinfo("d:/tmp/y"))

  message("... and add others later")
  system.time(ffsave(a, file="d:/tmp/z", move=TRUE))
  ffinfo("d:/tmp/z")

  message("let's delete/close/remove all objects")
  close(a)  # no file anymore, since we moved a into the ffarchive
  delete(b, df)
  rm(df, a, b, n)
  message("prove it")
  ls()

  message("restore all but ff files in a different directory")
  system.time(ffload("d:/tmp/x", rootpath="d:/tmp2"))
  lapply(ls(), function(i)filename(get(i)))

  delete(a, b, df)
  rm(df, a, b)

  ffdrop(c("d:/tmp/x", "d:/tmp/y", "d:/tmp/z"))
  
## End(Not run)