[R] princomp and prcomp confusion

[Liaw, Andy]

From: Patrick Connolly
> 
> When I look through archives at
> https://stat.ethz.ch/pipermail/r-help/2003-October/040525.html
> 
> I see this:
> 
> Liaw, Andy wrote:
> 
> >In the `Detail' section of ?princomp:
> >
> >princomp only handles so-called Q-mode PCA, that is feature 
> extraction 
> >of variables. If a data matrix is supplied (possibly via a 
> formula) it 
> >is required that there are at least as many units as variables. For 
> >R-mode PCA use prcomp.
> >
> 
> It doesn't appear that anyone disputed the accuracy of it.
> 
> 
> My current installation (version.string Version 2.3.1 
> (2006-06-01)) says in the detail of princomp
> 
> 
>      'princomp' only handles so-called R-mode PCA, that is feature
>      extraction of variables.  If a data matrix is supplied (possibly
>      via a formula) it is required that there are at least as many
>      units as variables.  For Q-mode PCA use 'prcomp'.
> 
> I've not been following principal components and have only 
> recently had a use for that methodology.  Am I to assume that 
> the later version is the correct one?  I thought I'd worked 
> out what the distinction between R-mode and Q-mode was, but 
> now I'm as confused as ever.

>From what I can gather by googling around about R-mode and Q-mode PCA, 
the current description should be the correct one.  

Andy


> best
> 
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