array {base}R Documentation

Multi-way Arrays

Description

Creates or tests for arrays.

Usage

array(data = NA, dim = length(data), dimnames = NULL)
as.array(x, ...)
is.array(x)

Arguments

data

a vector (including a list or expression vector) giving data to fill the array. Non-atomic classed objects are coerced by as.vector.

dim

the dim attribute for the array to be created, that is an integer vector of length one or more giving the maximal indices in each dimension.

dimnames

either NULL or the names for the dimensions. This must a list (or it will be ignored) with one component for each dimension, either NULL or a character vector of the length given by dim for that dimension. The list can be named, and the list names will be used as names for the dimensions. If the list is shorter than the number of dimensions, it is extended by NULLs to the length required.

x

an R object.

...

additional arguments to be passed to or from methods.

Details

An array in R can have one, two or more dimensions. It is simply a vector which is stored with additional attributes giving the dimensions (attribute "dim") and optionally names for those dimensions (attribute "dimnames").

A two-dimensional array is the same thing as a matrix.

One-dimensional arrays often look like vectors, but may be handled differently by some functions: str does distinguish them in recent versions of R.

The "dim" attribute is an integer vector of length one or more containing non-negative values: the product of the values must match the length of the array.

The "dimnames" attribute is optional: if present it is a list with one component for each dimension, either NULL or a character vector of the length given by the element of the "dim" attribute for that dimension.

is.array is a primitive function.

For a list array, the print methods prints entries of length not one in the form integer,7 indicating the type and length.

Value

array returns an array with the extents specified in dim and naming information in dimnames. The values in data are taken to be those in the array with the leftmost subscript moving fastest. If there are too few elements in data to fill the array, then the elements in data are recycled. If data has length zero, NA of an appropriate type is used for atomic vectors (0 for raw vectors) and NULL for lists.

Unlike matrix, array does not currently remove any attributes left by as.vector from a classed list data, so can return a list array with a class attribute.

as.array is a generic function for coercing to arrays. The default method does so by attaching a dim attribute to it. It also attaches dimnames if x has names. The sole purpose of this is to make it possible to access the dim[names] attribute at a later time.

is.array returns TRUE or FALSE depending on whether its argument is an array (i.e., has a dim attribute of positive length) or not. It is generic: you can write methods to handle specific classes of objects, see InternalMethods.

Note

is.array is a primitive function.

R 2.x.y allowed (although documented not to) a zero-length dim argument, and returned a vector of length one.

References

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

See Also

aperm, matrix, dim, dimnames.

Examples

dim(as.array(letters))
array(1:3, c(2,4)) # recycle 1:3 "2 2/3 times"
#     [,1] [,2] [,3] [,4]
#[1,]    1    3    2    1
#[2,]    2    1    3    2

[Package base version 2.15.3 Index]