[R] Plots with discontinuity balls

[Duncan Murdoch]

On 27/09/2007 8:04 PM, Paul Smith wrote:
> Dear All,
> 
> Can R plot graphs like the one at
> 
> http://www.mathwords.com/f/f_assets/floor_graph.gif
> 
> with the balls at the discontinuity points?

You can use segments() to draw the segments and symbols() to draw the 
balls.  For example,

plot(1,1,type='n', xlim=c(1,10), ylim=c(1,10))
segments(1:9, 1:9, 2:10, 1:9)
symbols(2:10, 1:9, circles=rep(0.1,9), inches=FALSE, bg="white",add=T)
symbols(1:9, 1:9, circles=rep(0.1,9), inches=FALSE, bg="black",add=T)

This depends on the order of drawing, because the white background of 
the first circles obscures the ends of the segments.

Duncan Murdoch