Serialization Interface for Single Objects

Description

Functions to write a single R object to a file, and to restore it.

Usage

saveRDS(object, file = "", ascii = FALSE, version = NULL,
        compress = TRUE, refhook = NULL)

readRDS(file, refhook = NULL)
infoRDS(file)

Arguments

Details

saveRDS and readRDS provide the means to save a single R object to a connection (typically a file) and to restore the object, quite possibly under a different name. This differs from save and load, which save and restore one or more named objects into an environment. They are widely used by R itself, for example to store metadata for a package and to store the help.search databases: the ".rds" file extension is most often used.

Functions serialize and unserialize provide a slightly lower-level interface to serialization: objects serialized to a connection by serialize can be read back by readRDS and conversely.

Function infoRDS retrieves meta-data about serialization produced by saveRDS or serialize. infoRDS cannot be used to detect whether a file is a serialization nor whether it is valid.

All of these interfaces use the same serialization format, but save writes a single line header (typically "RDXs\n") before the serialization of a single object (a pairlist of all the objects to be saved).

If file is a file name, it is opened by gzfile except for save(compress = FALSE) which uses file. Only for the exception are marked encodings of file which cannot be translated to the native encoding handled on Windows.

Compression is handled by the connection opened when file is a file name, so is only possible when file is a connection if handled by the connection. So e.g. url connections will need to be wrapped in a call to gzcon.

If a connection is supplied it will be opened (in binary mode) for the duration of the function if not already open: if it is already open it must be in binary mode for saveRDS(ascii = FALSE) or to read non-ASCII saves.

Value

For readRDS, an R object.

For saveRDS, NULL invisibly.

For infoRDS, an R list with elements version (version number, currently 2 or 3), writer_version (version of R that produced the serialization), min_reader_version (minimum version of R that can read the serialization), format (data representation) and native_encoding (native encoding of the session that produced the serialization, available since version 3). The data representation is given as "xdr" for big-endian binary representation, "ascii" for ASCII representation (produced via ascii = TRUE or ascii = NA) or "binary" (binary representation with native ‘endianness’ which can be produced by serialize).

Warning

Files produced by saveRDS (or serialize to a file connection) are not suitable as an interchange format between machines, for example to download from a website. The files produced by save have a header identifying the file type and so are better protected against erroneous use.

See Also

serialize, save and load.

The ‘R Internals’ manual for details of the format used.

Examples

fil <- tempfile("women", fileext = ".rds")
## save a single object to file
saveRDS(women, fil)
## restore it under a different name
women2 <- readRDS(fil)
identical(women, women2)
## or examine the object via a connection, which will be opened as needed.
con <- gzfile(fil)
readRDS(con)
close(con)

## Less convenient ways to restore the object
## which demonstrate compatibility with unserialize()
con <- gzfile(fil, "rb")
identical(unserialize(con), women)
close(con)
con <- gzfile(fil, "rb")
wm <- readBin(con, "raw", n = 1e4) # size is a guess
close(con)
identical(unserialize(wm), women)

## Format compatibility with serialize():
fil2 <- tempfile("women")
con <- file(fil2, "w")
serialize(women, con) # ASCII, uncompressed
close(con)
identical(women, readRDS(fil2))
fil3 <- tempfile("women")
con <- bzfile(fil3, "w")
serialize(women, con) # binary, bzip2-compressed
close(con)
identical(women, readRDS(fil3))

unlink(c(fil, fil2, fil3))