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\name{sparse3Darray}
\alias{sparse3Darray}
\title{
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{
\item{i,j,k}{
Integer vectors of equal length (or length 1), specifying the cells in the
array which have non-zero entries.
}
\item{x}{
Vector (numeric, integer, logical or complex)
of the same length as \code{i}, \code{j} and \code{k},
giving the values of the array entries that are not zero.
}
\item{dims}{
Dimension of the array. An integer vector of length 3.
}
\item{dimnames}{
Names for the three margins of the array. Either \code{NULL}
or a list of three character vectors.
}
\item{strict}{
Logical value specifying whether to enforce the rule that
each entry in \code{i,j,k,x} refers to a different cell.
If \code{strict=TRUE}, entries which refer to the same cell
in the array will be reduced to a single entry by summing the
\code{x} values. Default is \code{strict=FALSE}.
}
\item{nonzero}{
Logical value specifying whether to remove any entries
of \code{x} which equal zero.
}
}
\details{
An array \code{A} is three-dimensional if it is indexed by
three integer indices, so that \code{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 \pkg{spatstat.sparse} package defines the class
\code{sparse3Darray} of sparse three-dimensional arrays.
These arrays can have numeric, integer, logical, or complex
entries.
The function \code{sparse3Darray} creates an object of class
\code{"sparse3Darray"}. This object is essentially a list containing
the vectors \code{i,j,k,x} and the arguments \code{dims,dimnames}.
The arguments \code{i,j,k,x} should be vectors of equal length
identifying the cells in the array which have non-zero entries (indexed
by \code{i,j,k}) and giving the values in these cells (given by \code{x}).
The default behaviour of \code{sparse3Darray}
is to accept the arguments \code{i,j,k,x} without modifying them.
This would allow some entries of \code{x} to be equal to zero,
and would allow a cell in the array to be referenced more than once
in the indices \code{i,j,k}.
If \code{nonzero=TRUE}, entries will be removed if the \code{x} value
equals zero.
If \code{strict=TRUE}, entries which refer to the same cell in the
array will be combined into a single entry by summing the \code{x} values.
}
\value{
An object of class \code{"sparse3Darray"}.
}
\author{
\spatstatAuthors.
}
\seealso{
\code{\link{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)
}
\keyword{array}
\concept{sparse}
|
