subset.ppp: Extract Subset of Point Pattern

Description

Extract a subset of a point pattern, either by thinning the points or by trimming the window.

Usage

subset.ppp(x, subset, window, drop, ...)
  subset.ppp(x, subset, window)
  x[subset]
  x[subset,window]

Arguments

A two-dimensional point pattern. An object of class "ppp".

subset

logical vector indicating which points should be retained.

window

window (an object of class "owin") delineating a subset of the original observation window.

drop

Ignored - this argument is required for consistency with other methods for "[".

...

Ignored - this argument is required for consistency with other methods for "[".

Value

A point pattern (of class "ppp").

synopsis

subset.ppp(x, subset, window, drop, ...)

Warnings

The function does not check whether window is a subset of x$window.

Details

This function takes performs either ``thinning'' (retaining/deleting some points of a point pattern) or ``trimming'' (reducing the window of observation to a smaller subregion and retaining only those points which lie in the subregion). The pattern will be ``thinned'' if subset is specified. This should be a logical vector of length equal to the number of points in the point pattern x. The points (x$x[i], x$y[i]) for which subset[i]=TRUE will be retained, and the others will be deleted. The pattern will be ``trimmed'' if window is specified. This should be an object of class owin specifying a window of observation to which the point pattern x will be trimmed. The points of x lying inside the new window will be retained. Both ``thinning'' and ``trimming'' can be performed together.

Use the function unmark to remove marks from a marked point pattern.

Examples

Run this code

library(spatstat)

 data(longleaf)
 # Longleaf pines data
 plot(longleaf)
 # adult trees defined to have diameter at least 30 cm
 adult <- (longleaf$marks >= 30)
 longadult <- longleaf[adult]
 # equivalent to: longadult <- subset.ppp(longleaf, subset=adult)
 plot(longadult)
 # note that the marks are still retained.
 # Use unmark(longadult) to remove the marks
 
 # New Zealand trees data
 data(nztrees)
 plot(nztrees)          # plot shows a line of trees at the far right
 abline(v=148, lty=2)   # cut along this line
 nzw <- owin(c(0,148),c(0,95)) # the subwindow
 # trim dataset to this subwindow
 nzsub <- nztrees[,nzw]
 # equivalent to: nzsub <- subset.ppp(nztrees, window=nzw)
 plot(nzsub)

 # Redwood data
 data(redwood) 
 plot(redwood)
 # Random thinning: delete 60\% of data
 retain <- (runif(redwood$n) < 0.4)
 thinred <- redwood[retain]
 plot(thinred)

 # Lansing woods data - multitype points
 data(lansing)
 # hickory trees only
 hick <- lansing[lansing$marks == "hickory", ]
 # still a marked pattern -- remove marks
 hick <- unmark(hick)

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