Re: [R] help with PCA and classical scaling

From: Christian Hennig <chrish_at_stats.ucl.ac.uk>
Date: Sat 25 Jun 2005 - 04:44:34 EST

Hi Domenico,

multidimensional scaling methods (functions cmdscale, isoMDS, sammon) start with a dissimilarity matrix while PCA starts from a data matrix with variables. Equivalence of PCA and classical MDS refers to the situation where you use the Euclidean distances between the data points on which you apply PCA. (Note: I cite this from my memory, so check it before believing it.)

> My first question is: Do I need an initial embedding of my data before
> applying PCA through the methods princomp or prcomp in the stats package?

I don't think that you need PCA at all (depends on what exactly you want to do) - an MDS method alone could be enough for you (cmdscale, if you want to do something analogous to PCA).

Best,
Christian


R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Sat Jun 25 04:48:54 2005

This archive was generated by hypermail 2.1.8 : Fri 03 Mar 2006 - 03:33:02 EST