(De)compress I/O Through Connections
gzcon provides a modified connection that wraps an existing
connection, and decompresses reads or compresses writes through that
gzip headers are assumed.
gzcon(con, level = 6, allowNonCompressed = TRUE, text = FALSE)
- a connection.
- integer between 0 and 9, the compression level when writing.
- logical. When reading, should non-compressed input be allowed?
- logical. Should the connection be text-oriented? This is
distinct from the mode of the connection (must always be binary).
pushBackworks on the connection, otherwise
readBinand friends apply.
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
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. For this reason, the new connection needs to be closed explicitly.
An object inheriting from class
"connection". This is the same connection number as supplied, but with a modified internal structure. It has binary mode.
## 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 use 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")