[R] Distance between sets of points in transformed environmental space
Corrado
ct529 at york.ac.uk
Tue Dec 1 11:35:26 CET 2009
Thanks Mario! (Oppure grazie Mario?)
- Can those silhouette coefficients be used for distances between sets or only
for distances point to set?
- Where did you get the other post you attached? It did not come up when I
searched the mailing list!
Best,
On Tuesday 01 December 2009 10:31:47 Mario Valle wrote:
> silhouette coefficients?
> It measure for each point how similar is to its cluster other points and
> how dissimilar from the points of other clusters.
>
> P.N. Tam, M. Steinbach, V. Kumar, Introduction to data mining,
> Addison-Wesley, 2006 page 541
>
> Hope it helps.
> mario
>
> Charlotte Maia wrote:
> > Well, here's another naive post from me (hopefully better than the last
> > one).
> >
> > Firstly I'm not sure computing euclidean distance is that simple. I
> > would assume temperatures and precipitation would need to be
> > standardised in some way.
> >
> > I think the notion of how far away something is, and how distinct
> > location wise something is, are quite different, so maybe two
> > measures?
> >
> > For distance per se, I think your first idea is the best.
> > Plus simple is always good...
> >
> > For distinctness, given one one of two sets, for each point, you could
> > just compute the closest point to it. If the closest point is a member
> > of the same set, we will call that a + point, if the closest point is
> > a member of the other set, we will call it a - point. In principle the
> > measure of distinctness would be the sum of the +'s, however there
> > might need to be some scaling to take into account the number of
> > points in each set.
> >
> > There are also a lot of fancy things out there, so someone will
> > probably come up with a much fancier (and possibly better) idea than
> > this.
> >
> > Well, that's just my rant, before I go to bed.
> >
> >
> > kind regards
>
--
Corrado Topi
Global Climate Change & Biodiversity Indicators
Area 18,Department of Biology
University of York, York, YO10 5YW, UK
Phone: + 44 (0) 1904 328645, E-mail: ct529 at york.ac.uk
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