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\name{read_block_as_sparse}
\alias{read_block_as_sparse}
\alias{read_block_as_sparse,ANY-method}
\title{read_block_as_sparse}
\description{
\code{read_block_as_sparse()} is an internal generic function used by
\code{S4Arrays::\link[S4Arrays]{read_block}()} when \code{is_sparse(x)}
is \code{TRUE}.
}
\usage{
read_block_as_sparse(x, viewport)
\S4method{read_block_as_sparse}{ANY}(x, viewport)
}
\arguments{
\item{x}{
An array-like object for which \code{\link[S4Arrays]{is_sparse}(x)}
is \code{TRUE}.
}
\item{viewport}{
An \link[S4Arrays]{ArrayViewport} object compatible with \code{x},
that is, such that \code{refdim(viewport)} is identical to \code{dim(x)}.
}
}
\details{
Like \code{\link[S4Arrays]{read_block_as_dense}()} in the \pkg{S4Arrays}
package, \code{read_block_as_sparse()} is not meant to be called directly
by the end user. The end user should always call the higher-level
user-facing \code{\link[S4Arrays]{read_block}()} function instead.
See \code{?\link[S4Arrays]{read_block}} in the \pkg{S4Arrays} package
for more information.
Also, like \code{\link{extract_sparse_array}()},
\code{read_block_as_sparse()} should \emph{always} be called on
an array-like object \code{x} for which \code{is_sparse(x)} is
\code{TRUE}.
For maximum efficiency, \code{read_block_as_sparse()} methods should:
\enumerate{
\item NOT check that \code{\link[S4Arrays]{is_sparse}(x)} is \code{TRUE}.
\item NOT try to do anything with the dimnames on \code{x}
(\code{\link[S4Arrays]{read_block}()} takes care of that).
\item always operate natively on the sparse representation of the
data in \code{x}, that is, they should never \emph{expand}
it into a dense representation (e.g. with \emph{as.array()}).
}
}
\value{
A block of data as a \link{SparseArray} derivative (\link{COO_SparseArray}
or \link{SVT_SparseArray}) of the same \code{type()} as \code{x}.
}
\seealso{
\itemize{
\item \code{\link[S4Arrays]{read_block}} in the \pkg{S4Arrays} package
for the higher-level user-facing function for reading array blocks.
\item \link[S4Arrays]{ArrayGrid} in the \pkg{S4Arrays} package for
ArrayGrid and ArrayViewport objects.
\item \code{\link[S4Arrays]{is_sparse}} in the \pkg{S4Arrays} package
to check whether an object uses a sparse representation of the
data or not.
\item \link{SparseArray} objects.
\item \code{S4Arrays::\link[S4Arrays]{type}} in the \pkg{S4Arrays}
package to get the type of the elements of an array-like object.
\item \code{\link{extract_sparse_array}} for the workhorse behind
the default \code{read_block_as_sparse()} method.
\item \linkS4class{dgCMatrix} objects implemented in the \pkg{Matrix}
package.
}
}
\keyword{internal}
\keyword{array}
\keyword{methods}
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