save

Save R Objects

Description

save writes an external representation of R objects to the specified file. The objects can be read back from the file at a later date by using the function load (or data in some cases).

save.image() is just a short-cut for ‘save my current workspace’, i.e., save(list = ls(all = TRUE), file = ".RData"). It is also what happens with q("yes").

Usage

save(..., list = character(),
     file = stop("'file' must be specified"),
     ascii = FALSE, version = NULL, envir = parent.frame(),
     compress = !ascii, compression_level,
     eval.promises = TRUE, precheck = TRUE)

save.image(file = ".RData", version = NULL, ascii = FALSE,
           compress = !ascii, safe = TRUE)

Arguments

...

the names of the objects to be saved (as symbols or character strings).

list

A character vector containing the names of objects to be saved.

file

a (writable binary-mode) connection or the name of the file where the data will be saved (when tilde expansion is done). Must be a file name for save.image or version = 1.

ascii

if TRUE, an ASCII representation of the data is written. The default value of ascii is FALSE which leads to a binary file being written.

version

the workspace format version to use. NULL specifies the current default format. The version used from R 0.99.0 to R 1.3.1 was version 1. The default format as from R 1.4.0 is version 2.

envir

environment to search for objects to be saved.

compress

logical or character string specifying whether saving to a named file is to use compression. TRUE corresponds to gzip compression, and character strings "gzip", "bzip2" or "xz" specify the type of compression. Ignored when file is a connection and for workspace format version 1.

compression_level

integer: the level of compression to be used. Defaults to 6 for gzip compression and to 9 for bzip2 or xz compression.

eval.promises

logical: should objects which are promises be forced before saving?

precheck

logical: should the existence of the objects be checked before starting to save (and in particular before opening the file/connection)? Does not apply to version 1 saves.

safe

logical. If TRUE, a temporary file is used for creating the saved workspace. The temporary file is renamed to file if the save succeeds. This preserves an existing workspace file if the save fails, but at the cost of using extra disk space during the save.

See also

dput, dump, load, data.

For other interfaces to the underlying serialization format, see serialize and saveRDS.

Details

The names of the objects specified either as symbols (or character strings) in ... or as a character vector in list are used to look up the objects from environment envir. By default promises are evaluated, but if eval.promises = FALSE promises are saved (together with their evaluation environments). (Promises embedded in objects are always saved unevaluated.)

All R platforms use the XDR (bigendian) representation of C ints and doubles in binary save-d files, and these are portable across all R platforms. (ASCII saves used to be useful for moving data between platforms but are now mainly of historical interest. They can be more compact than binary saves where compression is not used, but are almost always slower to both read and write: binary saves compress much better than ASCII ones.)

Default values for the ascii, compress, safe and version arguments can be modified with the "save.defaults" option (used both by save and save.image), see also the ‘Examples’ section. If a "save.image.defaults" option is set it is used in preference to "save.defaults" for function save.image (which allows this to have different defaults).

A connection that is not already open will be opened in mode "wb".

Compression

Large files can be reduced considerably in size by compression. A particular 46MB object was saved as 35MB without compression in 2 seconds, 22MB with gzip compression in 8 secs, 19MB with bzip2 compression in 13 secs and 9.4MB with xz compression in 40 secs. The load times were 1.3, 2.8, 5.5 and 5.7 seconds respectively. These results are indicative, but the relative performances do depend on the actual file: xz compressed unusually well here.

It is possible to compress later (with gzip, bzip2 or xz) a file saved with compress = FALSE: the effect is the same as saving with compression. Also, a saved file can be uncompressed and re-compressed under a different compression scheme (and see resaveRdaFiles for a way to do so from within R).

Warnings

The ... arguments only give the names of the objects to be saved: they are searched for in the environment given by the envir argument, and the actual objects given as arguments need not be those found.

Saved R objects are binary files, even those saved with ascii = TRUE, so ensure that they are transferred without conversion of end of line markers and of 8-bit characters. The lines are delimited by LF on all platforms.

Although the default version has not changed since R 1.4.0, this does not mean that saved files are necessarily backwards compatible. You will be able to load a saved image into an earlier version of R unless use is made of later additions (for example, raw vectors or external pointers).

Note

The most common reason for failure is lack of write permission in the current directory. For save.image and for saving at the end of a session this will shown by messages like

    Error in gzfile(file, "wb") : unable to open connection
    In addition: Warning message:
    In gzfile(file, "wb") :
      cannot open compressed file '.RDataTmp',
      probable reason 'Permission denied'

Examples

x <- stats::runif(20)
y <- list(a = 1, b = TRUE, c = "oops")
save(x, y, file = "xy.RData")
save.image()
unlink("xy.RData")
unlink(".RData")

# set save defaults using option:
options(save.defaults = list(ascii = TRUE, safe = FALSE))
save.image()
unlink(".RData")
Documentation reproduced from package base, version 3.0.1, License: Part of R 3.0.1