This help topic is for R version 2.9.0. For the current version of R, try https://stat.ethz.ch/R-manual/R-patched/library/base/html/gzcon.html
gzcon {base}R Documentation

(De)compress I/O Through Connections

Description

gzcon provides a modified connection that wraps an existing connection, and decompresses reads or compresses writes through that connection. Standard gzip headers are assumed.

Usage

gzcon(con, level = 6, allowNonCompressed = TRUE)

Arguments

con

a connection.

level

integer between 0 and 9, the compression level when writing.

allowNonCompressed

logical. When reading, should non-compressed input be allowed?

Details

If con is open then the modified connection is opened. Closing the wrapper connection will also close the underlying connection.

Reading from a connection which does not supply a gzip magic header is equivalent to reading from the original connection if allowNonCompressed is true, otherwise an error.

The original connection becomes unusable: any object pointing to it will now refer to the modified connection.

When the connection is opened for reading, the input is expected to start with the gzip magic header. If it does not and if allowNonCompressed = TRUE (the default) the input is read as-is.

Value

An object inheriting from class "connection". This is the same connection number as supplied, but with a modified internal structure. It has binary mode.

See Also

gzfile

Examples

## Uncompress a data file from a URL
z <- gzcon(url("http://www.stats.ox.ac.uk/pub/datasets/csb/ch12.dat.gz"))
# read.table can only read from a text-mode connection.
raw <- textConnection(readLines(z))
close(z)
dat <- read.table(raw)
close(raw)
dat[1:4, ]


## gzfile and gzcon can inter-work.
## Of course here one would used gzfile, but file() can be replaced by
## any other connection generator.
zz <- gzfile("ex.gz", "w")
cat("TITLE extra line", "2 3 5 7", "", "11 13 17", file = zz, sep = "\n")
close(zz)
readLines(zz <- gzcon(file("ex.gz", "rb")))
close(zz)
unlink("ex.gz")


zz <- gzcon(file("ex2.gz", "wb"))
cat("TITLE extra line", "2 3 5 7", "", "11 13 17", file = zz, sep = "\n")
close(zz)
readLines(zz <- gzfile("ex2.gz"))
close(zz)
unlink("ex2.gz")

[Package base version 2.9.0 ]