Lattice panel function for two rug plots

This panel function is defined to plot two rugs, one on top of the other in a multi-panel lattice display.

panel.doublerug(
  xa = NULL,
  xb = NULL,
  regular = TRUE,
  start = if (regular) 0 else 0.97,
  end = if (regular) 0.03 else 1,
  x.units = rep("npc", 2),
  lty = 1,
  lwd = 1
)

Arguments

xa, xb	Numeric vectors to be plotted.
regular	Logical flag indicating whether rug is to be drawn on the usual side (bottom/left) as opposed to the other side (top/right).
start, end	Start and end points for the rug ticks on the y-axis.
x.units	Character vectors, replicated to be of length two. Specifies the (grid) units associated with start and end above. x.units are for the rug on the x-axis and y-axis respectively (and thus are associated with start and end values on the y and x scales respectively). See panel.rug for more details.
lty, lwd	Line type and width arguments (see par for more details).