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\name{linearInd}
\alias{linearInd}
\title{Converting array indices into linear indices}
\description{
\code{linearInd} performs the reverse conversion of
\code{base::\link[base]{arrayInd}}, that is, it converts so-called
\emph{array indices} (i.e. n-uplets) into \emph{linear indices}.
}
\usage{
linearInd(aind, dim)
}
\arguments{
\item{aind}{
Typically a numeric matrix like one returned by
\code{base::\link[base]{arrayInd}}, that is, a matrix where
each row is an n-uplet representing an array index.
Each array index must describe a position relative to the
implicit array i.e. to the array whose dimensions are specified
via the \code{dim} argument.
For convenience, \code{aind} can also be specified as a vector with
one element per dimension in the implicit array, in which case it will
be treated like a 1-row matrix.
Note that no bounds checking is performed, that is, values in the j-th
column of \code{aind} can be < 1 or > \code{dim[j]}.
}
\item{dim}{
An integer vector containing the dimensions of the underlying array.
Note that \code{dim} can also be an integer matrix, in which case it
must have the same shape as \code{aind}, that is, 1 row per row in
\code{aind} and 1 column per dimension.
}
}
\value{
An integer vector with one element per row in \code{aind} if
\code{aind} is a matrix.
A single integer if \code{aind} is a vector.
}
\seealso{
\code{\link[base]{arrayInd}} in the \pkg{base} package for the reverse
conversion.
}
\examples{
dim <- 4:2
linearInd(c(4, 3, 1), dim)
linearInd(c(4, 3, 2), dim)
aind <- rbind(c(1, 1, 1),
c(2, 1, 1),
c(3, 1, 1),
c(4, 1, 1),
c(1, 2, 1),
c(1, 1, 2),
c(4, 3, 2))
linearInd(aind, dim)
## With a matrix of dimensions:
dims <- rbind(c(4L, 3L),
c(5L, 3L),
c(6L, 3L))
aind <- rbind(c(1, 2),
c(1, 2),
c(1, 2))
linearInd(aind, dims)
## Sanity checks:
dim <- c(33:30, 45L, 30L)
stopifnot(linearInd(rep(1, 6), dim) == 1)
stopifnot(linearInd(dim, dim) == prod(dim))
stopifnot(identical(linearInd(arrayInd(1:120, 6:4), 6:4), 1:120))
stopifnot(identical(linearInd(arrayInd(840:1, 4:7), 4:7), 840:1))
}
\keyword{utilities}
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