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\name{extract_array}
\alias{extract_array}
\alias{extract_array,ANY-method}
\alias{extract_array,array-method}
\alias{extract_array,data.frame-method}
\alias{extract_array,DataFrame-method}
\alias{type,ANY-method}
\alias{as.array.Array}
\alias{as.array,Array-method}
\alias{as.matrix.Array}
\alias{as.matrix,Array-method}
\alias{as.data.frame.Array}
\alias{as.data.frame,Array-method}
\alias{as.vector.Array}
\alias{as.vector,Array-method}
\alias{as.logical.Array}
\alias{as.logical,Array-method}
\alias{as.integer.Array}
\alias{as.integer,Array-method}
\alias{as.numeric.Array}
\alias{as.numeric,Array-method}
\alias{as.complex.Array}
\alias{as.complex,Array-method}
\alias{as.character.Array}
\alias{as.character,Array-method}
\alias{as.raw.Array}
\alias{as.raw,Array-method}
\title{extract_array}
\description{
\code{extract_array} is an internal generic function not aimed to be used
directly by the user. It has methods defined for array, data.frame,
\link[S4Vectors]{DataFrame} objects and other array-like objects.
The \code{DelayedArray()} constructor function will accept any seed that
complies with the \emph{seed contract} i.e. that supports \code{dim()},
\code{dimnames()}, and \code{extract_array()}.
}
\usage{
extract_array(x, index)
type(x)
}
\arguments{
\item{x}{
An array-like object.
}
\item{index}{
An unnamed list of subscripts as positive integer vectors, one vector
per dimension in \code{x}. Empty and missing subscripts (represented
by \code{integer(0)} and \code{NULL} list elements, respectively) are
allowed. The subscripts can contain duplicated indices. They cannot
contain NAs or non-positive values.
}
}
\details{
\code{extract_array} methods need to support empty and missing subscripts
e.g. \code{extract_array(x, list(NULL, integer(0)))} must return an M x 0
matrix and \code{extract_array(x, list(integer(0), integer(0)))} a 0 x 0
matrix.
Also subscripts are allowed to contain duplicated indices so things like
\code{extract_array(seed, list(c(1:3, 3:1), 2L))} need to be supported.
\code{type(x)} returns the type of the elements in \code{x}. It's equivalent
to \code{typeof(x)} or \code{storage.mode(x)} on an ordinary array or vector.
It works out-of-the-box on any array-like object \code{x} for which
\code{extract_array(x)} works.
}
\value{
\code{extract_array} must return an \emph{ordinary} array of the
appropriate type (i.e. integer, double, etc...). For example, if
\code{x} is an object representing an M x N matrix of complex numbers,
\code{extract_array(x, list(NULL, 2L))} must return its 2nd column as
an \emph{ordinary} M x 1 matrix of type complex.
\code{type} returns the type of the array elements.
}
\seealso{
\itemize{
\item \code{\link{read_block}}.
\item \link[base]{array} and \link[base]{data.frame} objects in base R.
\item \link[S4Vectors]{DataFrame} objects in the \pkg{S4Vectors} package.
\item \link{DelayedArray} objects.
}
}
\examples{
## Coming soon...
}
\keyword{internal}
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