[R] xyplot and lsegments

[Alex Brown]

Hi,

	How might I use xyplot to plot segments where the segments are in the  
input data? (ie a directed acyclic forest).

	Here's an example in base graphics:

n = data.frame(id = c(1,2,3,4), parent = c(0,1,2,2), value =  
c(5,5.5,7,3), date = c(1,2,3,3.5))

plot(n$date, n$value)

do.call(
  segments,
  with(
    merge(n,n,by.x="parent", by.y="id"),
    data.frame(x0=date.x, y0=value.x, x1=date.y, y1=value.y)
  )
)

	xyplot only seems to take an x and a y, and panels only seem to get x  
and y.

	I can see an lsegments, but I can't see how to use it in this example.

-Alex