Hi,
one possibility would be to calculate the convex hull using chull(). I
believe that the hull points are returned by chull() in a clockwise
order (?), so the points between the rightmost and the leftmost point in
the chull() result are the lower half of the convex hull. Remove these
points from the original dataset (a variant of "peeling convex hulls")
and iterate until you have removed your prespecified percentage of
points - these all lie outside of the final lower hull (though the
percentage will, of course, only be approximated, but you should be able
to modify this to taste).
HTH
Stephan
David Winsemius schrieb:
On Jun 30, 2010, at 2:05 PM, Asha Sharma wrote:
Hi,
I am looking for a way to find the lower envelope of points on a plot,
preferably specifying what percentage of points should be allowed to
lie outside the envelope. There must be a straightforward way to do
this, but I do not seem to be able to find it. I would greatly
appreciate any help.
You probably want something like the "lower half" of the convex hull.
You should find quite a bit of code with your favorite r search engine
on the topic of "convex hull".
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