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Dots objects: lists of quotations.

Source: R/dots.R, R/conversions.R, R/force.R
dots.Rd

d <- dots(a = one, b = two) captures each of its arguments, unevaluated, in a dots object (a named list of quotations).

as.data.frame.dots transforms the contents of a dots object into a data frame with one row per quotation, with columns:

  • name: a character,

  • expr: an expression,

  • env: an environment object or NULL if forced,

  • value: NULL or a value if forced.

forced_dots(...) forces its arguments and constructs a dots object with forced quotations.

forced_dots_(values) creates a dots object from a list of values

Usage

dots(...)

dots_(exprs, envs)

exprs(d)

# S3 method for dots
exprs(d)

exprs(d) <- value

# S3 method for dots
exprs(d) <- value

envs(d)

# S3 method for dots
envs(d)

envs(d) <- value

# S3 method for dots
[(x, ..., drop = FALSE)

# S3 method for dots
[(x, ...) <- value

# S3 method for dots
c(...)

# S3 method for quotation
c(...)

# S3 method for dots
as.data.frame(x, row.names = NULL, ...)

forced_dots(...)

forced_dots_(values)

Arguments

...

Any number of arguments.

exprs

An expression or list of expressions.

envs

An environment or list of environments.

d

A dots object.

value

A replacement value or list of values.

x

A dots object.

drop

See Extract.

row.names

If not given, uses make.unique(x$name)

values

A list; each element will be used as data.

Value

dots(...) constructs a list with class 'dots', each element of which is a quotation.

dots_(exprs, envs) constructs a dots object given lists of expressions and environments. (To construct a dots object from quotation objects, use c().)

exprs(d) extracts a list of expressions from a dots object.

The mutator exprs(d) <- value returns a new dots object with the new expressions.

envs(d) extracts a list of environments from a dots object.

envs(d) returns a named list of environments.

envs(d) <- value returns an updated dots object with the environments replaced with the new value(s).

as.data.frame.dots returns a data frame.

Details

Objects of class "dots" mirror R's special variable .... Unlike ..., a dots is:

  • immutable (evaluating does not change it),

  • first-class (you can give it any name, not just ...),

  • data (The R interpreter treates it as literal data rather than triggering argument splicing).

d <- dots(...) is used to capture the contents of ... without triggering evaluation. This improves on as.list(substitute(...())) by capturing the environment of each argument along with their expressions. (You can also use get_dots().)

Note

The columns have a class "oneline" for better printing.

Examples


named.list <- function(...) {
 # Collect only named arguments, ignoring unnamed arguments.
 d <- dots(...)
 do(list, d[names(d) != ""])
}

named.list(a=1, b=2*2, stop("this is not evaluated"))
#> $a
#> [1] 1
#> 
#> $b
#> [1] 4
#>