Data is read via connection interfaces. Connections can be to files or URLs, for example.
file, opens a connection to a filegzfile, opens a link to a gzipped filebzfile, opens a link to a file compressed with bzip2url, opens a link to a web page
To connect to a file
> str(file)
function (description = '', open = '', blocking = TRUE,
encoding = getOption("encoding"))
The description is the name of the file, and open is a code indicating:
- “r” read only
- “w” write (and initialization of a new file)
- “a” append
- “rb”, “wb”, “ab” read,write, or append in binary mode (Windows)
In general, shortcuts are powerful tools for navigating files. In practice, we often do not need to interact with the connection interface directly.
con <- file('foo.txt', 'r')
data <- read.csv(con)
close(con)
is equivalent to
data <- read.csv("foo.txt")
read per line of a text file
con <- gzfile("example.gz")
x <- readLines(con, 10)
writeLines takes a vector of characters and writes each element one line at a time to a text file.
readLines can be useful for line-by-line reading of web pages
con <- url("http://google.com", "r")
x <- readLines(con)