Extract.lpp: Extract Subset of Point Pattern on Linear Network

Description

Extract a subset of a point pattern on a linear network.

Usage

"["(x, i, j, drop=FALSE, ..., snip=TRUE)

Arguments

A point pattern on a linear network (object of class "lpp").

Subset index. A valid subset index in the usual R sense, indicating which points should be retained.

Spatial window (object of class "owin") delineating the region that should be retained.

drop

Logical value indicating whether to remove unused levels of the marks, if the marks are a factor.

snip

Logical. If TRUE (the default), segments of the network which cross the boundary of the window j will be cut by the boundary. If FALSE, these segments will be deleted.

...

Ignored.

Value

A point pattern on a linear network (of class "lpp").

Details

This function extracts a designated subset of a point pattern on a linear network.

The function [.lpp is a method for [ for the class "lpp". It extracts a designated subset of a point pattern. The argument 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 x. In the latter case, the points (x$x[i], x$y[i]) for which subset[i]=TRUE will be retained, and the others will be deleted.

The argument j, if present, should be a spatial window. The pattern inside the region will be retained. Line segments that cross the boundary of the window are deleted in the current implementation.

The argument 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 snip specifies what to do with segments of the network which cross the boundary of the window j. If snip=FALSE, such segments are simply deleted. If snip=TRUE (the default), such segments are cut into pieces by the boundary of j, and those pieces which lie inside the window ji are included in the resulting network.

Use unmark to remove all the marks in a marked point pattern, and subset.lpp to remove only some columns of marks.

Examples

Run this code

  # 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)