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\name{Extract.lpp}
\alias{[.lpp}
\title{Extract Subset of Point Pattern on Linear Network}
\description{
Extract a subset of a point pattern on a linear network.
}
\usage{
\method{[}{lpp}(x, i, j, drop=FALSE, \dots, snip=TRUE)
}
\arguments{
\item{x}{
A point pattern on a linear network (object of class \code{"lpp"}).
}
\item{i}{
Subset index. A valid subset index in the usual \R sense,
indicating which points should be retained.
}
\item{j}{
Spatial window
(object of class \code{"owin"}) delineating the region that should
be retained.
}
\item{drop}{
Logical value indicating whether to remove unused levels
of the marks, if the marks are a factor.
}
\item{snip}{
Logical. If \code{TRUE} (the default), segments of the network
which cross the boundary of the window \code{j} will be cut by the boundary.
If \code{FALSE}, these segments will be deleted.
}
\item{\dots}{
Ignored.
}
}
\value{
A point pattern on a linear network (of class \code{"lpp"}).
}
\details{
This function extracts a designated subset of a point pattern
on a linear network.
The function \code{[.lpp} is a method for \code{\link{[}} for the
class \code{"lpp"}. It extracts a designated subset of a point pattern.
The argument \code{i} should be a subset index in the usual \R sense:
either a numeric vector
of positive indices (identifying the points to be retained),
a numeric vector of negative indices (identifying the points
to be deleted) or a logical vector of length equal to the number of
points in the point pattern \code{x}. In the latter case,
the points \code{(x$x[i], x$y[i])} for which
\code{subset[i]=TRUE} will be retained, and the others
will be deleted.
The argument \code{j}, if present, should be a spatial window.
The pattern inside the region will be retained.
\emph{Line segments that cross the boundary of the window
are deleted} in the current implementation.
The argument \code{drop} determines whether to remove
unused levels of a factor, if the point pattern is multitype
(i.e. the marks are a factor) or if the marks are a data frame or hyperframe
in which some of the columns are factors.
The argument \code{snip} specifies what to do with segments of
the network which cross the boundary of the window \code{j}.
If \code{snip=FALSE}, such segments are simply deleted.
If \code{snip=TRUE} (the default), such segments are cut into pieces by the
boundary of \code{j}, and those pieces which lie inside the window
\code{ji} are included in the resulting network.
Use \code{\link[spatstat.geom]{unmark}} to remove all the marks in a marked point
pattern, and \code{\link{subset.lpp}} to remove only some columns of marks.
}
\seealso{
\code{\link{lpp}},
\code{\link{subset.lpp}}
}
\examples{
# Chicago crimes data - remove cases of assault
chicago[marks(chicago) != "assault"]
# equivalent to subset(chicago, select=-assault)
# spatial window subset
B <- owin(c(350, 700), c(600, 1000))
plot(chicago)
plot(B, add=TRUE, lty=2, border="red", lwd=3)
op <- par(mfrow=c(1,2), mar=0.6+c(0,0,1,0))
plot(B, main="chicago[B, snip=FALSE]", lty=3, border="red")
plot(chicago[, B, snip=FALSE], add=TRUE)
plot(B, main="chicago[B, snip=TRUE]", lty=3, border="red")
plot(chicago[, B, snip=TRUE], add=TRUE)
par(op)
}
\author{
\adrian
and
\rolf
}
\keyword{spatial}
\keyword{manip}
\concept{Linear network}
|
