vec_size: Number of observations

In vctrs: Vector Helpers

Number of observations

Description

vec_size(x) returns the size of a vector. vec_is_empty() returns TRUE if the size is zero, FALSE otherwise.

The size is distinct from the length() of a vector because it generalises to the "number of observations" for 2d structures, i.e. it's the number of rows in matrix or a data frame. This definition has the important property that every column of a data frame (even data frame and matrix columns) have the same size. vec_size_common(...) returns the common size of multiple vectors.

list_sizes() returns an integer vector containing the size of each element of a list. It is nearly equivalent to, but faster than, map_int(x, vec_size), with the exception that list_sizes() will error on non-list inputs, as defined by obj_is_list(). list_sizes() is to vec_size() as lengths() is to length().

Usage

vec_size(x)

vec_size_common(
  ...,
  .size = NULL,
  .absent = 0L,
  .arg = "",
  .call = caller_env()
)

list_sizes(x)

vec_is_empty(x)

Arguments

x, ...	Vector inputs or NULL.
.size	If NULL, the default, the output size is determined by recycling the lengths of all elements of .... Alternatively, you can supply .size to force a known size; in this case, x and ... are ignored.
.absent	The size used when no input is provided, or when all input is NULL. If left as NULL when no input is supplied, an error is thrown.
.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.

Details

There is no vctrs helper that retrieves the number of columns: as this is a property of the type.

vec_size() is equivalent to NROW() but has a name that is easier to pronounce, and throws an error when passed non-vector inputs.

Value

An integer (or double for long vectors).

vec_size_common() returns .absent if all inputs are NULL or absent, 0L by default.

Invariants

• vec_size(dataframe) == vec_size(dataframe[[i]])

• vec_size(matrix) == vec_size(matrix[, i, drop = FALSE])

• vec_size(vec_c(x, y)) == vec_size(x) + vec_size(y)

The size of NULL

The size of NULL is hard-coded to 0L in vec_size(). vec_size_common() returns .absent when all inputs are NULL (if only some inputs are NULL, they are simply ignored).

A default size of 0 makes sense because sizes are most often queried in order to compute a total size while assembling a collection of vectors. Since we treat NULL as an absent input by principle, we return the identity of sizes under addition to reflect that an absent input doesn't take up any size.

Note that other defaults might make sense under different circumstances. For instance, a default size of 1 makes sense for finding the common size because 1 is the identity of the recycling rules.

Dependencies

• vec_proxy()

See Also

vec_slice() for a variation of [ compatible with vec_size(), and vec_recycle() to recycle vectors to common length.

Examples

vec_size(1:100)
vec_size(mtcars)
vec_size(array(dim = c(3, 5, 10)))

vec_size_common(1:10, 1:10)
vec_size_common(1:10, 1)
vec_size_common(integer(), 1)

list_sizes(list("a", 1:5, letters))

vctrs documentation built on May 29, 2024, 11:39 a.m.