[R] PCA and categorical data

Mark Difford mark_difford at yahoo.co.uk
Fri Mar 6 11:17:56 CET 2009

Hi Galandis,

dudi.mix() in package ade4 does PCA using categorical and/or quantitative
variables. Ordered cats are replaced by poly(x, deg=2). Squares of
categoricals can also be used. The method is a generalization by Chessel of
the method of Hill and Smith.

Regards, Mark.

Galanidis Alexandros wrote:
> Hi all,
> I' m trying to figure out if it is appropriate to do a PCA having only
> categorical data (not ordinal). I have only find the following quote:
> One method to find such relationships is to select appropriate variables
> and
> to view the data using a method like Principle Components Analysis (PCA)
> [4].
> This approach gives us a clear picture of the data using KL-plot of the
> PCA.
> However, the method is not settled for the data including categorical
> data.
> [http://hp.vector.co.jp/authors/VA038807/personal/covEigGiniRep17.pdf]
> but I'm still not sure if it WRONG to do so.
> Any opinion or reference would be very helpful
> thanks
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