| % File src/library/base/man/deparse.Rd |
| % Part of the R package, https://www.R-project.org |
| % Copyright 1995-2018 R Core Team |
| % Distributed under GPL 2 or later |
| |
| \name{deparse} |
| \alias{deparse} |
| \title{Expression Deparsing} |
| \description{ |
| Turn unevaluated expressions into character strings. |
| } |
| \usage{ |
| deparse(expr, width.cutoff = 60L, |
| backtick = mode(expr) \%in\% c("call", "expression", "(", "function"), |
| control = c("keepNA", "keepInteger", "niceNames", "showAttributes"), |
| nlines = -1L) |
| } |
| \arguments{ |
| \item{expr}{any \R expression.} |
| \item{width.cutoff}{integer in \eqn{[20, 500]} determining the cutoff |
| (in bytes) at which line-breaking is tried.} |
| \item{backtick}{logical indicating whether symbolic names should be |
| enclosed in backticks if they do not follow the standard syntax.} |
| \item{control}{character vector (or \code{NULL}) of deparsing options. |
| See \code{\link{.deparseOpts}}.} |
| \item{nlines}{integer: the maximum number of lines to produce. |
| Negative values indicate no limit.} |
| } |
| \details{ |
| This function turns unevaluated expressions (where \sQuote{expression} |
| is taken in a wider sense than the strict concept of a vector of mode |
| \code{"expression"} used in \code{\link{expression}}) into character |
| strings (a kind of inverse to \code{\link{parse}}). |
| |
| A typical use of this is to create informative labels for data sets |
| and plots. The example shows a simple use of this facility. It uses |
| the functions \code{deparse} and \code{substitute} to create labels |
| for a plot which are character string versions of the actual arguments |
| to the function \code{myplot}. |
| |
| The default for the \code{backtick} option is not to quote single |
| symbols but only composite expressions. This is a compromise to |
| avoid breaking existing code. |
| |
| Using \code{control = "all"} comes closest to making \code{deparse()} |
| an inverse of \code{parse()}. However, not all objects are |
| deparse-able even with this option and a warning will be issued if the |
| function recognizes that it is being asked to do the impossible. |
| |
| Numeric and complex vectors are converted using 15 significant digits: |
| see \code{\link{as.character}} for more details. |
| |
| \code{width.cutoff} is a lower bound for the line lengths: deparsing a |
| line proceeds until at least \code{width.cutoff} \emph{bytes} have |
| been output and e.g.\sspace{}\code{arg = value} expressions will not be split |
| across lines. |
| } |
| \note{ |
| To avoid the risk of a source attribute out of sync with the actual |
| function definition, the source attribute of a function will never |
| be deparsed as an attribute. |
| |
| Deparsing internal structures may not be accurate: for example the |
| graphics display list recorded by \code{\link{recordPlot}} is not |
| intended to be deparsed and \code{.Internal} calls will be shown as |
| primitive calls. |
| } |
| \references{ |
| Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) |
| \emph{The New S Language}. |
| Wadsworth & Brooks/Cole. |
| } |
| \seealso{ |
| \code{\link{substitute}}, |
| \code{\link{parse}}, |
| \code{\link{expression}}. |
| |
| \code{Quotes} for quoting conventions, including backticks. |
| } |
| \examples{ |
| require(stats); require(graphics) |
| |
| deparse(args(lm)) |
| deparse(args(lm), width = 500) |
| myplot <- |
| function(x, y) { |
| plot(x, y, xlab = deparse(substitute(x)), |
| ylab = deparse(substitute(y))) |
| } |
| e <- quote(`foo bar`) |
| deparse(e) |
| deparse(e, backtick = TRUE) |
| e <- quote(`foo bar`+1) |
| deparse(e) |
| deparse(e, control = "all") # wraps it w/ quote( . ) |
| } |
| \keyword{programming} |
| \keyword{manip} |
| \keyword{data} |