[R] loadings or summary in Principal components

Berton Gunter gunter.berton at gene.com
Thu Mar 31 20:22:04 CEST 2005

(R 2.0.1)

summary() gives the correct results.

The print.loadings() print method is just giving the squared length of each
of the eigenvectors, which is 1 by definition, of course. I don't know
whether this is a bug or intentional, but it certainly seems silly. 

In general, it is good practice to use summary() and other supplied
extraction methods for obtaining information about a fitted object rather
than directly accessing the components themselves (however, I, too, often
violate this rule of thumb).

Finally, prcomp() is the preferred way of doing PCA in R, as the princomp
documentation says. The fit object has no "loadings" component and therefore
no problem.

-- Bert Gunter
Genentech Non-Clinical Statistics
South San Francisco, CA
"The business of the statistician is to catalyze the scientific learning
process."  - George E. P. Box

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Adrian Katschke
> Sent: Thursday, March 31, 2005 7:47 AM
> To: RHelp
> Subject: [R] loadings or summary in Principal components
> May be a simple question, but not understanding why in 
> princomp I get different results for loadings and summary for 
> my eigenvectors and eigenvalues. 
> When I use pc.cr$loadings using the USArrests dataset the 
> proportion of variance is equal for each of the components, 
> but when summary(pc.cr) is used the proportion of variance is 
> showing different proportions. My question is why do they 
> differ? I thought that they would report the same thing?
> Thanks in advance for clearing this confusion for me.
> Adrian Katschke
> 	[[alternative HTML version deleted]]
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