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 files (lacking the gzip magic header) 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 is unusable: any object pointing to it will now refer to the modified connection.

Value

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

See Also

gzfile

Examples

## Not run: ## This example may not still be available
## print the value to see what objects were created.
con <- url("http://hesweb1.med.virginia.edu/biostat/s/data/sav/kprats.sav")
print(load(con))
## End(Not run)

## 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")))
close(zz)
unlink("ex.gz")

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

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