deparse {base}

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)

deparse1(expr, collapse = " ", width.cutoff = 500L, ...)

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 (or NULL) of deparsing options. control = "all" is thorough, see .deparseOpts.

nlines

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

collapse

a string, passed to paste().

...

further arguments passed to deparse().

Details

These functions turn unevaluated expressions (where ‘expression’ is taken in a wider sense than the strict concept of a vector of mode and type (typeof) "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.

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.

deparse1() is a simple utility added in R 4.0.0 to ensure a string result (character vector of length one), typically used in name construction, as deparse1(substitute(.)).

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 recordPlot is not intended to be deparsed and .Internal calls will be shown as primitive calls.

References

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

See Also

.deparseOpts for available control settings; dput() and dump() for related functions using identical internal deparsing functionality.

substitute, parse, expression.

Quotes for quoting conventions, including backticks.

Examples

require(stats); require(graphics)

deparse(args(lm))
deparse(args(lm), width.cutoff = 500)

myplot <- function(x, y) {
    plot(x, y, xlab = deparse1(substitute(x)),
               ylab = deparse1(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( . )