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.
- object to be coerced or tested.
- a logical indicating whether to copy all values or (default) only those whose names do not begin with a dot.
Almost all lists in R internally are Generic Vectors, whereas traditional dotted pair lists (as in LISP) remain available but rarely seen by users (except as
formals of functions).
The arguments to
pairlist are of the form
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
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") for a non-list, methods for
as.vector may be invoked.
as.list turns a factor into a list of one-element factors. Attributes may be dropped unless the argument already is a list or expression. (This is inconsistent with functions such as
as.character which always drop attributes, and is for efficiency since lists can be expensive to copy.)
"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 enclosing environments are searched. (Objects copied are duplicated so this can be an expensive operation.) Note that there is an inverse operation, the
as.environment() method for list objects.
as.pairlist is implemented as
as.vector(x, "pairlist"), and hence will dispatch methods for the generic function
as.vector. Lists are copied element-by-element into a pairlist and the names of the list used as tags for the pairlist: the return value for other types of argument is undocumented.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
‘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)
Documentation reproduced from R 3.0.2. License: GPL-2.