obj_is_list: List checks

In vctrs: Vector Helpers

List checks

Description

• obj_is_list() tests if x is considered a list in the vctrs sense. It returns TRUE if all of the following hold:

  • x must have list storage, i.e. typeof(x) returns "list"

  • x must not have a dim attribute

  • x must not have a class attribute, or must explicitly inherit from "list" as the last class

• list_all_vectors() takes a list and returns TRUE if all elements of that list are vectors.

• list_all_size() takes a list and returns TRUE if all elements of that list have the same size.

• list_all_recyclable() takes a list and returns TRUE if all elements of that list can recycle to size.

• obj_check_list(), list_check_all_vectors(), list_check_all_size(), and list_check_all_recyclable() use the above functions, but throw a standardized and informative error if they return FALSE.

Usage

obj_is_list(x)

obj_check_list(x, ..., arg = caller_arg(x), call = caller_env())

list_all_vectors(x, ..., allow_null = FALSE)

list_check_all_vectors(
  x,
  ...,
  allow_null = FALSE,
  arg = caller_arg(x),
  call = caller_env()
)

list_all_size(x, size, ..., allow_null = FALSE)

list_check_all_size(
  x,
  size,
  ...,
  allow_null = FALSE,
  arg = caller_arg(x),
  call = caller_env()
)

list_all_recyclable(x, size, ..., allow_null = FALSE)

list_check_all_recyclable(
  x,
  size,
  ...,
  allow_null = FALSE,
  arg = caller_arg(x),
  call = caller_env()
)

Arguments

x	For ⁠vec_*()⁠ functions, an object. For ⁠list_*()⁠ functions, a list.
...	These dots are for future extensions and must be empty.
arg	An argument name as a string. This argument will be mentioned in error messages as the input that is at the origin of a problem.
call	The execution environment of a currently running function, e.g. caller_env(). The function will be mentioned in error messages as the source of the error. See the call argument of abort() for more information.
allow_null	Whether NULL elements should be skipped over automatically or not.
size	The size to check each element for compatibility with.

Details

Notably, data frames and S3 record style classes like POSIXlt are not considered lists.

See Also

list_sizes()

Examples

obj_is_list(list())
obj_is_list(list_of(1))
obj_is_list(data.frame())

list_all_vectors(list(1, mtcars))
list_all_vectors(list(1, environment()))

list_all_size(list(1:2, 2:3), 2)
list_all_size(list(1:2, 2:4), 2)

list_all_recyclable(list(1, 2:3), 2)
list_all_recyclable(list(1, 2:4), 2)

# `list_`-prefixed functions assume a list:
try(list_all_vectors(environment()))

# `NULL` elements are not considered vectors and generally have a size of 0
try(list_check_all_vectors(list(1, NULL, 2)))
try(list_check_all_size(list(1, NULL, 2), size = 1))

# However, it is often useful to perform upfront vector/size checks on a
# list, excluding `NULL`s, and then filter them out later on
list_check_all_vectors(list(1, NULL, 2), allow_null = TRUE)
list_check_all_size(list(1, NULL, 2), size = 1, allow_null = TRUE)

# Performing the checks before removing `NULL`s from the list ensures that
# any errors report the correct index. Note how the index is incorrect from a
# user's point of view if we filter out `NULL` too soon.
xs <- list(1, NULL, 2:3)
try(list_check_all_size(xs, size = 1, allow_null = TRUE))
xs <- vec_slice(xs, !vec_detect_missing(xs))
try(list_check_all_size(xs, size = 1))

vctrs documentation built on Jan. 24, 2026, 1:07 a.m.