Re: [R] help with PCA and classical scaling

From: Christian Hennig <>
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).

Christian mailing list PLEASE do read the posting guide! 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