list(...) pairlist(...) as.list(x) as.list.default(x) as.pairlist(x) is.list(x) is.pairlist(x) alist(...)
The arguments to list
or pairlist
are of the form
value
or tag=value
.
The functions return a list composed of its arguments
with each value either tagged or untagged,
depending on how the argument was specified.
alist
is like list
, except in the handling of tagged
arguments with no value. These are handled as if they described
function arguments with no default (cf. formals
), whereas
list
simply ignores them.
as.list
attempts to coerce its argument to list type.
For functions, this returns the concatenation of the list of formals
arguments and the function body. For expressions, the list of
constituent calls is returned.
is.list
returns TRUE
iff its argument
is a list
or a pairlist
of length
> 0,
whereas is.pairlist
only returns TRUE
in the latter case.
An empty pairlist, pairlist()
is the same as NULL
. This
is different from list()
.
vector(., mode="list")
, c
, for concatenation;
formals
.data(cars) # create a plotting structure pts <- list(x=cars[,1], y=cars[,2]) plot(pts) # Argument lists f <- function()x # Note the specification of a "..." argument: formals(f) <- al <- alist(x=, y=2, ...=) f str(al) str(pl <- as.pairlist(ps.options())) ## These are all TRUE: is.list(pl) && is.pairlist(pl) !is.null(list()) is.null(pairlist()) !is.list(NULL) is.pairlist(pairlist()) is.null(as.pairlist(list())) is.null(as.pairlist(NULL))