[R] How to combine to PCAs

Ravi Varadhan RVaradhan at jhmi.edu
Thu Jun 5 15:40:35 CEST 2008

Let  V = (v11, v12, ..., v1n, v21, v22, ..., v2n) be the matrix of data with
2*n columns.  Now, you simply do PCA on this data matrix.  
See the following paper, which has a related example:

Gabriel, K. R. and Odoroff, C. L. (1990). Biplots in biomedical research.
Statistics in Medicine, 9, 469-485. 


-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
Behalf Of Stefan Koenig
Sent: Thursday, June 05, 2008 4:47 AM
To: r-help at r-project.org
Subject: [R] How to combine to PCAs

Dear all:

Subjects were measured two times (t1 and t2) on different variables (v1 ...
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

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