Is an Object Atomic or Recursive?

Description

is.atomic returns TRUE if x is of an atomic type and FALSE otherwise. is.atomic(NULL) returns FALSE since R version 4.4.0.

is.recursive returns TRUE if x has a recursive (list-like) structure and FALSE otherwise.

Usage

is.atomic(x)
is.recursive(x)

Arguments

Details

is.atomic is true for the atomic types ("logical", "integer", "numeric", "complex", "character" and "raw").

Most types of objects are regarded as recursive. Exceptions are the atomic types, NULL, symbols (as given by as.name), S4 objects with slots, external pointers, and—rarely visible from R—weak references and byte code, see typeof.

It is common to call the atomic types ‘atomic vectors’, but note that is.vector imposes further restrictions: an object can be atomic but not a vector (in that sense).

These are primitive functions.

References

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

See Also

is.list, is.language, etc, and the demo("is.things").

Examples

require(stats)

is.a.r <- function(x) c(is.atomic(x), is.recursive(x))

is.a.r(c(a = 1, b = 3)) # TRUE FALSE
is.a.r(list())          # FALSE TRUE - a list is a list
is.a.r(list(2))         # FALSE TRUE
is.a.r(lm)              # FALSE TRUE
is.a.r(y ~ x)           # FALSE TRUE
is.a.r(expression(x+1)) # FALSE TRUE
is.a.r(quote(exp))      # FALSE FALSE
is.a.r(NULL)            # FALSE FALSE

# Reproduce pre-4.4 behavior of is.atomic()
is.atomicN <- function(x) is.atomic(x) || is.null(x)
is.atomicN(NULL) # TRUE