[R] biplot & identify

Gavin Simpson gavin.simpson at ucl.ac.uk
Fri Jul 23 12:07:48 CEST 2004

Wolski wrote:
> Hi!
> Is there a way to get biplot and identify to work togheter.
> Having the output of prcomp I would like to draw a biplot that. 
> Instead of plotting the sample (row-names) names plots some "pch"
> symbols. (thats easy with xlabs)
> But now I would like to add using identify the names to only some of
> the points. I have noticed that both biplot.prcomp and biplot.default
> does a lot of scaling.
> So has anyone a function like identify.prcomp please?
> Is it possible?

Yes, take a look at Jari Oksanen's vegan package
http://cc.oulu.fi/~jarioksa/softhelp/vegan.html and on CRAN.

The ordiplot function can be used to plot ordination diagrams including
those from prcomp. There is an identify method for ordiplot that allows
you to label points - you need to store the ordiplot object before using
identify, e.g.:

exmp.pc <- prcomp(some.data)
exmp.ord <- ordiplot(exmp.pc)
identify(exemp.ord, what = "sites")

see ?ordiplot and the example which includes the use of identify.

> Sincerely Eryk



Gavin Simpson                     [T] +44 (0)20 7679 5522
ENSIS Research Fellow             [F] +44 (0)20 7679 7565
ENSIS Ltd. & ECRC                 [E] gavin.simpson at ucl.ac.uk
UCL Department of Geography       [W] http://www.ucl.ac.uk/~ucfagls/cv/
26 Bedford Way                    [W] http://www.ucl.ac.uk/~ucfagls/
London.  WC1H 0AP.

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