[R] changing pen mode [or adjusting for overlapping points?]

Don Armstrong don at donarmstrong.com
Tue Mar 11 22:11:40 CET 2003

On Tue, 11 Mar 2003, Marc Schwartz wrote:
> I may be mis-understanding what you are trying to do, but if you are
> using plot() to generate a scatter plot (as opposed to a density
> plot) and there are actual overlapping points between the two sets,
> you could use jitter() to introduce some random noise into the
> plotted points.

jitter is a good idea, but in this case, the problem is the density of
the ploted points themselves. Just adding noise do much in this case.

[So that it's more clear what the problem is, I've stuck a graph up at
http://rzlab.ucr.edu/images/test.png. Ideally you should be able to
decern where the red region stops underneath the green [while at the
same time seeing that the green has outliers below it.]

There is a mode in photoshop called multiply that does something
similar, but I'm not sure if there is a postscript mode that does the
same thing. [Editing the postscript file itself is not a problem if
that's the only solution...]

Don Armstrong

My spelling ability, or rather the lack thereof, is one of the wonders
of the modern world.

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