These are methods for the generic function unique for
point pattern datasets (of class "ppp", see
ppp.object, or class "ppx").
This function removes duplicate points in x,
and returns a point pattern.
Two points in a point pattern are deemed to be identical
if their \(x,y\) coordinates are the same,
and their marks are the same (if they carry marks).
This is the default rule: see duplicated.ppp
for other options.