[R] Difference between prcomp and cmdscale

[Mark Difford]

Michael,

Why should that confuse you?  Have you tried reading some of the literature
on these methods?  There's plenty about them on the Net (Wiki's often a
goodish place to start)---and even in R, if you're prepared to look ;).

BestR,
Mark.


michael watson (IAH-C) wrote:
> 
> I'm looking for someone to explain the difference between these
> procedures.  The function prcomp() does principal components anaylsis,
> and the function cmdscale() does classical multi-dimensional scaling
> (also called principal coordinates analysis).
> 
> My confusion stems from the fact that they give very similar results:
> 
> my.d <- matrix(rnorm(50), ncol=5)
> rownames(my.d) <- paste("c", 1:10, sep="")
> # prcomp
> prc <- prcomp(my.d)
> # cmdscale
> mds <- cmdscale(dist(my.d))
> cor(prc$x[,1], mds[,1]) # produces 1 or -1
> cor(prc$x[,2], mds[,2]) # produces 1 or -1
> 
> Presumably, under the defaults for these commands in R, they carry out
> the same (or very similar) procedures?
> 
> Thanks
> Mick
> 
> The information contained in this message may be confidentia...{{dropped}}
> 
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