Re: [R] How to combine to PCAs

From: Mark Difford <mark_difford_at_yahoo.co.uk>
Date: Thu, 05 Jun 2008 04:45:16 -0700 (PDT)

Hi Stefan,

>> Is it possible to combine both PCAs in order to get only one set of >> eigenvectors?

Yes there is: statis() in the ade4 package is probably what you want. In short, it does a k-table analysis that will give you a common ordination/position. It also shows how each time-set deviates from that common position. RV-coeff. showing how well the two tables match each other &c. Excellent graphical summaries...

The method is quite complex, but if you read French then there is some very good documentation on their site:

http://pbil.univ-lyon1.fr/ADE-4

Here you will also find a couple of papers (in English) on the method. There's also a list. Stephane (Dray) replies to many of the questions and writes and speaks English well.

HTH, Mark.

Stefan Koenig wrote:
>
> Dear all:
>
> Subjects were measured two times (t1 and t2) on different variables (v1
> ... vn).
> Between t1 and t2 there was an experimental manipulation. I computed two
> PCAs for time-points t1 and t2.
>
> Is it possible to combine both PCAs in order to get only one set of
> eigenvectors? Due to the experimental manipulation measurement values on
> time points t1 and t2 changed for each subject.
>
> Many thanks
> Stefan
> --
>
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