[R] Using hexbin to Eliminate Indiscernible Points from a Plot

[Steve Dutky]

Dear all,
I have installed hexbin 1.1-4 package and cobbled together 
the following function, cull, to eliminate xy points closer 
than a specified resolution.   While it appears to reduce the 
congestion of points on a plot, I am surprised to see 
overlapping points remain.

I would appreciate any insight as to what may cause this and 
as to whether a better way to reduce plot congestion may exist.

Thanks, Steve Dutky
sdutky at terpalum.umd.edu
+1-301-545-4113

"cull"<-function(x,y,PAR=par(),resolution=PAR$cin[1]/2) {
#
# returns a logical vector of points that are discernible at 
# the specified resolution.

# requires that either that PAR argument be passed explicity 
# as named list of "cin" and "pin" parameters or that active 
# graphics device already sized for plotting x and y

# PARS$pin == width X height of plot areas in inches
   bins<-ceiling(PAR$pin/resolution)[1]
   shape<-PAR$pin[2]/PAR$pin[1]

   if (missing(y))  #assume x has two columns
      !duplicated(hexbin(x[,1],x[,2],xbins=bins,shape=shape,IDs=T)@cID)
   else
      !duplicated(hexbin(x,y,xbins=bins,shape=shape,IDs=T)@cID)


}

#example:
library(hexbin)
m<-cbind(rnorm(10000),rnorm(10000))
plot(apply(m,2,FUN=range))
k<-cull(m, resolution=9/72)
plot(m[k,])