`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 `vec_is_list()`

. `list_sizes()`

is
to `vec_size()`

as `lengths()`

is to `length()`

.

vec_size(x) vec_size_common(..., .size = NULL, .absent = 0L) list_sizes(x) vec_is_empty(x)

x, ... | Vector inputs or |
---|---|

.size | If |

.absent | The size used when no input is provided, or when all input
is |

An integer (or double for long vectors).

`vec_size_common()`

returns `.absent`

if all inputs are `NULL`

or
absent, `0L`

by default.

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.

`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`

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.

`vec_slice()`

for a variation of `[`

compatible with `vec_size()`

,
and `vec_recycle()`

to recycle vectors to common length.

vec_size(1:100) #> [1] 100 vec_size(mtcars) #> [1] 32 vec_size(array(dim = c(3, 5, 10))) #> [1] 3 vec_size_common(1:10, 1:10) #> [1] 10 vec_size_common(1:10, 1) #> [1] 10 vec_size_common(integer(), 1) #> [1] 0 list_sizes(list("a", 1:5, letters)) #> [1] 1 5 26