[R] Hide line ends behind unfilled circles?

[Marc Schwartz]

On Sun, 2006-10-15 at 11:21 -0400, Michael Kubovy wrote:
> Dear r-helpers,
> 
> xx <- c(0.000, 0.210, 0.714, 0.514, 1.000, 0.190, 0.590, 0.152)
> yy <- c(0.000, 0.265, 0.256, 0.521, 0.538, 0.761, 0.821, 1.000)
> aa <- c(19, 19, 19, 21, 19, 21, 21, 21)
> x0 <- xx[c(1, 1, 2, 2, 2, 3, 3, 4, 4, 4, 5, 6, 6, 7)]
> y0 <- yy[c(1, 1, 2, 2, 2, 3, 3, 4, 4, 4, 5, 6, 6, 7)]
> x1 <- xx[c(2, 3, 3, 4, 6, 4, 5, 5, 6, 7, 7, 7, 8, 8)]
> y1 <- yy[c(2, 3, 3, 4, 6, 4, 5, 5, 6, 7, 7, 7, 8, 8)]
> 
> plot(yy ~ xx, pch = aa, cex = 3)
> segments(x0, y0, x1, y1)
> 
> Can anyone suggest a way of insuring that the lines are hidden behind  
> the unfilled circles?

Try this:

 # Set up the plot region
 plot(yy ~ xx, type = "n")
 
 # Draw the segments first
 segments(x0, y0, x1, y1)

 # Set the circle (pch) background colors
 col <- c(rep("black", 3), "white", "black", rep("white", 3))

 # Now draw the circles over the line intersections
 points(xx, yy, pch = 21, bg = col, cex = 3)


The "unfilled" circles in this case are actually solid white or black.
So instead of altering the point character (pch), we alter the colors.

HTH,

Marc Schwartz