textConnection {base}R Documentation

Text Connections

Description

Input and output text connections.

Usage

textConnection(object, open = "r", local = FALSE)

Arguments

object character. A description of the connection. For an input this is an R character vector object, and for an output connection the name for the R character vector to receive the output.
open character. Either "r" (or equivalently "") for an input connection or "w" or "a" for an output connection.
local logical. Used only for output connections. If TRUE, output is assigned to a variable in the calling environment. Otherwise the global environment is used.

Details

An input text connection is opened and the character vector is copied at time the connection object is created, and close destroys the copy.

An output text connection is opened and creates an R character vector of the given name in the user's workspace or in the calling environment, depending on the value of the local argument. This object will at all times hold the completed lines of output to the connection, and isIncomplete will indicate if there is an incomplete final line. Closing the connection will output the final line, complete or not. (A line is complete once it has been terminated by end-of-line, represented by "\n" in R.)

Opening a text connection with mode = "a" will attempt to append to an existing character vector with the given name in the user's workspace or the calling environment. If none is found (even if an object exists of the right name but the wrong type) a new character vector wil be created, with a warning.

You cannot seek on a text connection, and seek will always return zero as the position.

Value

A connection object of class "textConnection" which inherits from class "connection".

Note

As output text connections keep the character vector up to date line-by-line, they are relatively expensive to use, and it is often better to use an anonymous file() connection to collect output.

On platforms where vsnprintf does not return the needed length of output (e.g., Windows) there is a 100,000 character limit on the length of line for output connections: longer lines will be truncated with a warning.

See Also

connections, showConnections, pushBack, capture.output.

Examples

zz <- textConnection(LETTERS)
readLines(zz, 2)
scan(zz, "", 4)
pushBack(c("aa", "bb"), zz)
scan(zz, "", 4)
close(zz)

zz <- textConnection("foo", "w")
writeLines(c("testit1", "testit2"), zz)
cat("testit3 ", file=zz)
isIncomplete(zz)
cat("testit4\n", file=zz)
isIncomplete(zz)
close(zz)
foo

## Not run: 
# capture R output: use part of example from help(lm)
zz <- textConnection("foo", "w")
ctl <- c(4.17, 5.58, 5.18, 6.11, 4.5, 4.61, 5.17, 4.53, 5.33, 5.14)
trt <- c(4.81, 4.17, 4.41, 3.59, 5.87, 3.83, 6.03, 4.89, 4.32, 4.69)
group <- gl(2, 10, 20, labels = c("Ctl", "Trt"))
weight <- c(ctl, trt)
sink(zz)
anova(lm.D9 <- lm(weight ~ group))
cat("\nSummary of Residuals:\n\n")
summary(resid(lm.D9))
sink()
close(zz)
cat(foo, sep = "\n")
## End(Not run)

[Package base version 2.1.0 Index]