list {base} | R Documentation

## Lists - Generic and Dotted Pairs

### Description

Functions to construct, coerce and check for all kinds of R lists.

### Usage

    list(...)
    pairlist(...)

    as.list(x, ...)
    as.pairlist(x)
    as.list.environment(x, all.names=FALSE, ...)

    is.list(x)
    is.pairlist(x)

    alist(...)

### Arguments

`...` | objects.
`x` | object to be coerced or tested.
`all.names` | a logical indicating whether to copy all values in `as.list.environment`/

### Details

Most lists in R internally are Generic Vectors, whereas traditional dotted pair lists (as in LISP) are still available.

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.

`is.list` and `is.pairlist` are generic: you can write methods to handle specific classes of objects, see InternalMethods.

`as.list.environment` copies the named values from an environment to a list. The user can request that all named objects are copied (normally names that begin with a dot are not). The output is not sorted and no parent environments are searched.

An empty pairlist, `pairlist()` is the same as `NULL`. This is different from `list()`.

### References

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

### See Also

`vector(., mode="list")`, `c`, for concatenation; `formals`.

### Examples

    # 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
    al

    ##environment->list coercion

    e1 <- new.env()
    e1$a <- 10
    e1$b <- 20
    as.list(e1)

[Package base version 2.1.1 Index]