Re: Windows line plotting

[David L Lorenz <lorenz@usgs.gov>]

Thom,
  I have also found this to be
a troubling characteristic of the GUI graphics. Plotting a large number
of points is fast and easy, but wanting specialized treatments by groups
is difficult and sometimes very slow. You can break the lines by writing
a user function to smooth the data. Here's one that works for a 2D plot.
It does not smooth the data, but does insert breaks when brk (the id) changes.

breaklines <- function(x,y,z, brk,
...) {
 xs <- tapply(x, brk, function(x)
c(x,NA))
 ys <- tapply(y, brk, function(x)
c(x,NA))
 return(list(x=unlist(xs), y=unlist(ys)))
}

  The z argument is ignored, but
conceivably could be used in a 3-D plot. In the Line/Scatterplot menu dialog
window, on the Smooth/Sort page, select Smoothing type User, enter breaklines
in the Function Name box, and brk=DF$id in the Other Arguments box, where
DF is the name of the data frame. Then press the Apply button. Of course
this must be after the breaklines function has been sourced.
Dave