deparse: 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("keepInteger", "showAttributes", "keepNA"), nlines = -1L)

Arguments

expr

any R expression.

width.cutoff

integer in $[20, 500]$ determining the cutoff (in bytes) at which line-breaking is tried.

backtick

logical indicating whether symbolic names should be enclosed in backticks if they do not follow the standard syntax.

control

character vector of deparsing options. See .deparseOpts.

nlines

integer: the maximum number of lines to produce. Negative values indicate no limit.

Details

This function turns unevaluated expressions (where ‘expression’ is taken in a wider sense than the strict concept of a vector of mode "expression" used in expression) into character strings (a kind of inverse to 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 deparse and substitute to create labels for a plot which are character string versions of the actual arguments to the function myplot.

The default for the backtick option is not to quote single symbols but only composite expressions. This is a compromise to avoid breaking existing code.

Using control = "all" comes closest to making deparse() an inverse of 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 as.character for more details.

width.cutoff is a lower bound for the line lengths: deparsing a line proceeds until at least width.cutoff bytes have been output and e.g. arg = value expressions will not be split across lines.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

Examples

Run this code

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")

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