[R] How to combine to PCAs

Mark Difford mark_difford at yahoo.co.uk
Thu Jun 5 13:45:16 CEST 2008

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:


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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