R help - May 2007 - Biplot

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Hi,

If you check the help for princomp, you'll see that it returns all
sorts of information in the form of a list. The most convenient
way is to save your analysis
xresults <- princomp(x, cor=TRUE)
then you can look at the scores, plot them yourself, anything
else you want
xscores <- xresults$scores

and so on.

Sarah

On 5/13/07, Soare Marcian-Alin <soarealin at gmail.com>
wrote:
> Hello everybody,
>
> How could I extract the components of of a PCA to plot it into a biplot?
> I want to make pairwise biplots of the first three main components:
>
> biplot(princomp(x, cor=TRUE))
> biplot(princomp(x[,c(1,2)], cor=TRUE))
> biplot(princomp(x[,c(1,3)], cor=TRUE))
> biplot(princomp(x[,c(2,3)], cor=TRUE))
>
> Is this the only way, how I could plot them?
> I thought, that it could be possible to extract them of the full PCA ..
>
> KR,
> Alin
>
-- 
Sarah Goslee
http://www.functionaldiversity.org

The PCA of two variables out of three is unrelated to the PCA of all 
three, so your example code does not do what you describe.

If you want to plot two of the components of a full PCA, see
?biplot.princomp: and note that it says this is not a true biplot for 
other than the first two components.

(And really you should have been able to find this yourself: please do 
study the posting guide.)

On Sun, 13 May 2007, Soare Marcian-Alin wrote:
> Hello everybody,
>
> How could I extract the components of of a PCA to plot it into a biplot?
> I want to make pairwise biplots of the first three main components:
>
> biplot(princomp(x, cor=TRUE))
> biplot(princomp(x[,c(1,2)], cor=TRUE))
> biplot(princomp(x[,c(1,3)], cor=TRUE))
> biplot(princomp(x[,c(2,3)], cor=TRUE))
>
> Is this the only way, how I could plot them?
> I thought, that it could be possible to extract them of the full PCA ..
>
> KR,
> Alin
>
> 	[[alternative HTML version deleted]]
>
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> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595