sparse3Darray {spatstat.sparse}

Create a Sparse Three-Dimensional Array

Description

Create a sparse representation of a three-dimensional array.

Usage

sparse3Darray(i = integer(0), j = integer(0), k = integer(0),
              x = numeric(0),
              dims = c(max(i), max(j), max(k)), dimnames = NULL,
              strict = FALSE, nonzero = FALSE)

Arguments

i, j, k

Integer vectors of equal length (or length 1), specifying the cells in the array which have non-zero entries.

x

Vector (numeric, integer, logical or complex) of the same length as i, j and k, giving the values of the array entries that are not zero.

dims

Dimension of the array. An integer vector of length 3.

dimnames

Names for the three margins of the array. Either NULL or a list of three character vectors.

strict

Logical value specifying whether to enforce the rule that each entry in i,j,k,x refers to a different cell. If strict=TRUE, entries which refer to the same cell in the array will be reduced to a single entry by summing the x values. Default is strict=FALSE.

nonzero

Logical value specifying whether to remove any entries of x which equal zero.

Details

An array A is three-dimensional if it is indexed by three integer indices, so that A[i,j,k] specifies an element of the array. The array is called sparse if only a small fraction of the entries are non-zero. A sparse array can be represented economically by listing only the entries which are non-zero.

The spatstat.sparse package defines the class sparse3Darray of sparse three-dimensional arrays. These arrays can have numeric, integer, logical, or complex entries.

The function sparse3Darray creates an object of class "sparse3Darray". This object is essentially a list containing the vectors i,j,k,x and the arguments dims,dimnames.

The arguments i,j,k,x should be vectors of equal length identifying the cells in the array which have non-zero entries (indexed by i,j,k) and giving the values in these cells (given by x).

The default behaviour of sparse3Darray is to accept the arguments i,j,k,x without modifying them. This would allow some entries of x to be equal to zero, and would allow a cell in the array to be referenced more than once in the indices i,j,k.

If nonzero=TRUE, entries will be removed if the x value equals zero.

If strict=TRUE, entries which refer to the same cell in the array will be combined into a single entry by summing the x values.

Value

An object of class "sparse3Darray".

Author(s)

Adrian Baddeley [e-mail], Rolf Turner [e-mail] and Ege Rubak [e-mail].

See Also

as.sparse3Darray

Examples

  ## creation by specifying nonzero elements
  M <- sparse3Darray(i=1:3, j=c(3,1,2), k=4:2,
                     x=runif(3), dims=rep(4, 3))
  M
  ## duplicate entries
  Mn <- sparse3Darray(i=c(1,1,2), j=c(2,2,1), k=c(3,3,2),
                     x=runif(3), dims=rep(3, 3))
  ## cumulate entries in duplicate positions
  Ms <- sparse3Darray(i=c(1,1,2), j=c(2,2,1), k=c(3,3,2),
                      x=runif(3), dims=rep(3, 3), strict=TRUE)