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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Do not modify this file since it was automatically generated from:
%
% captureOutput.R
%
% by the Rdoc compiler part of the R.oo package.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\name{captureOutput}
\alias{captureOutput}
\title{Evaluate an R expression and captures the output}
\description{
Evaluate an R expression and captures the output.
}
\usage{
captureOutput(expr, file=NULL, append=FALSE, collapse=NULL, envir=parent.frame())
}
\arguments{
\item{expr}{The R expression to be evaluated.}
\item{file}{A file name or a \code{\link[base:connections]{connection}} to where the output is
directed. Alternatively, if \code{\link[base]{NULL}} the output is captured to
and returned as a \code{\link[base]{character}} \code{\link[base]{vector}}.}
\item{append}{If \code{\link[base:logical]{TRUE}}, the output is appended to the file or
the (unopened) connection, otherwise it overwrites.}
\item{collapse}{A \code{\link[base]{character}} string used for collapsing the captured
rows. If \code{\link[base]{NULL}}, the rows are not collapsed.}
\item{envir}{The \code{\link[base]{environment}} in which the expression is evaluated.}
}
\value{
Returns captured output as a \code{\link[base]{character}} \code{\link[base]{vector}}.
}
\details{
This method imitates \code{\link[utils]{capture.output}} with the major
difference that it captures strings via a \code{\link[base]{raw}} connection rather
than via internal strings. The latter becomes exponentially slow
for large outputs [1,2].
}
\examples{
# captureOutput() is much faster than capture.output()
# for large outputs when capturing to a string.
for (n in c(10e3, 20e3, 30e3, 40e3)) {
printf("n=\%d\n", n)
x <- rnorm(n)
t0 <- system.time({
bfr0 <- capture.output(print(x))
})
print(t0)
t1 <- system.time({
bfr <- captureOutput(print(x))
})
print(t1)
print(t1/t0)
bfr2n <- captureOutput(print(x), collapse="\n")
bfr2r <- captureOutput(print(x), collapse="\r")
stopifnot(identical(bfr, bfr0))
} # for (n ...)
}
\author{Henrik Bengtsson}
\seealso{
Internally, \code{\link[base]{eval}}() is used to evaluate the expression.
and \code{\link[utils]{capture.output}} to capture the output.
}
\references{
[1] R-devel thread 'capture.output(): Using a rawConnection() [linear]
instead of textConnection() [exponential]?', 2014-02-04.
\url{https://stat.ethz.ch/pipermail/r-devel/2014-February/068349.html}
[2] JottR blog post 'PERFORMANCE: captureOutput() is much faster than
capture.output()', 2015-05-26.
\url{https://www.jottr.org/2014/05/26/captureoutput/}
}
\keyword{IO}
\keyword{programming}
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