\name{unique.ppp}
\alias{unique.ppp}
\title{Extract Unique Points from a Spatial Point Pattern}
\description{
  Removes any points that are identical to other points
  in a spatial point pattern.
}
\usage{
 \method{unique}{ppp}(x, \dots)
}
\arguments{
  \item{x}{
    A spatial point pattern
    (object of class \code{"ppp"}).
  }
  \item{\dots}{
    Ignored.
  }
}
\value{
  Another point pattern object.
}
\details{
  This is a method for the generic function \code{unique} for 
  point pattern datasets (of class \code{"ppp"}, see \code{\link{ppp.object}}).

  Two points in a point pattern are deemed to be identical
  if their \eqn{x,y} coordinates are the same,
  and their marks are also the same (if they carry marks).
  The Examples section illustrates how it is possible for
  a point pattern to contain a pair of identical points.

  This function removes duplicate points in \code{x},
  and returns a point pattern.
}
\seealso{
  \code{\link{ppp.object}},
  \code{\link{duplicated.ppp}},
  \code{\link{multiplicity.ppp}}
}
\examples{
   X <- ppp(c(1,1,0.5), c(2,2,1), window=square(3))
   unique(X)
}

\author{Adrian Baddeley
  \email{adrian@maths.uwa.edu.au}
  \url{http://www.maths.uwa.edu.au/~adrian/}
  and Rolf Turner
  \email{r.turner@auckland.ac.nz}
}
\keyword{spatial}
\keyword{methods}