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\name{clump}
\alias{clump}
\alias{clump,RasterLayer-method}
\title{Detect clumps}
\description{
Detect clumps (patches) of connected cells. Each clump gets a unique ID. NA and zero are used as background values (i.e. these values are used to separate clumps). You can use queen's or rook's case, using the \code{directions} argument. For larger files that are processed in chunks, the highest clump number is not necessarily equal to the number of clumps (unless you use argument \code{gaps=FALSE}).
}
\usage{
\S4method{clump}{RasterLayer}(x, filename="", directions=8, gaps=TRUE, ...)
}
\arguments{
\item{x}{RasterLayer}
\item{filename}{Character. Filename for the output RasterLayer (optional)}
\item{directions}{Integer. Which cells are considered adjacent? Should be 8 (Queen's case) or 4 (Rook's case) }
\item{gaps}{Logical. If \code{TRUE} (the default), there may be 'gaps' in the chunk numbers (e.g. you may have clumps with IDs 1, 2, 3 and 5, but not 4). If it is \code{FALSE}, these numbers will be recoded from 1 to n (4 in this example)}
\item{...}{Additional arguments as for \code{\link{writeRaster}}}
}
\note{
This function requires that the igraph package is available.
}
\value{
RasterLayer
}
\author{Robert J. Hijmans and Jacob van Etten}
\examples{
r <- raster(ncols=12, nrows=12)
set.seed(0)
values(r) <- round(runif(ncell(r))*0.7 )
rc <- clump(r)
freq(rc)
plot(rc)
}
\keyword{spatial}
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