| list {base} | R Documentation |
Functions to construct, coerce and check for both kinds of R lists.
list(...)
pairlist(...)
as.list(x, ...)
## S3 method for class 'environment'
as.list(x, all.names = FALSE, ...)
as.pairlist(x)
is.list(x)
is.pairlist(x)
alist(...)
... |
objects, possibly named. |
x |
object to be coerced or tested. |
all.names |
a logical indicating whether to copy all values or (default) only those whose names do not begin with a dot. |
Most lists in R internally are Generic Vectors, whereas
traditional dotted pair lists (as in LISP) are available
but rarely seen by users (except as formals of functions).
The arguments to list or pairlist are of the form
value or tag=value. The functions return a list or
dotted pair list composed of its arguments with each value either
tagged or untagged, depending on how the argument was specified.
alist handles its arguments as if they described function
arguments. So the values are not evaluated, and tagged arguments with
no value are allowed whereas list simply ignores them.
alist is most often used in conjunction with formals.
as.list attempts to coerce its argument to a list. For
functions, this returns the concatenation of the list of formal
arguments and the function body. For expressions, the list of
constituent elements is returned. as.list is generic, and as the
default method calls as.vector(mode="list") methods for
as.vector may be invoked. as.list
turns a factor into a list of one-element factors. All attributes
will be dropped unless the argument already is a list. (This is
inconsistent with functions such as as.character, and is
for efficiency since lists can be expensive to copy.)
is.list returns TRUE if and only if its argument
is a list or a pairlist of length > 0.
is.pairlist returns TRUE if and only if the argument
is a pairlist or NULL (see below).
The "environment" method for as.list copies the
name-value pairs (for names not beginning with a dot) from an
environment to a named list. The user can request that all named
objects are copied. The list is in no particular order (the order
depends on the order of creation of objects and whether the
environment is hashed). No parent environments are searched. (Objects
copied are duplicated so this can be an expensive operation.)
An empty pairlist, pairlist() is the same as NULL. This
is different from list().
as.pairlist is implemented as as.vector(x, "pairlist"),
and hence will dispatch methods for the generic function as.vector.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
vector("list", length) for creation of a list with empty
components; c, for concatenation; formals.
unlist is an approximate inverse to as.list().
‘plotmath’ for the use of list in plot annotation.
require(graphics)
# create a plotting structure
pts <- list(x=cars[,1], y=cars[,2])
plot(pts)
is.pairlist(.Options) # a user-level pairlist
## "pre-allocate" an empty list of length 5
vector("list", 5)
# Argument lists
f <- function() x
# Note the specification of a "..." argument:
formals(f) <- al <- alist(x=, y=2+3, ...=)
f
al
## environment->list coercion
e1 <- new.env()
e1$a <- 10
e1$b <- 20
as.list(e1)