[R] Signs of loadings from princomp on Windows

[Francisco Chamu]

I have run this on both Windows 2000 and XP.  All I did was install
the binaries from CRAN so I think I am using the standard Rblas.dll.

To reproduce what I see you must run the code at the beginning of the
R session.  After the second run, all subsequent runs give the same
result as the second set.

Thanks,
Francisco


On Tue, 14 Sep 2004 08:29:25 +0200, Uwe Ligges
<ligges at statistik.uni-dortmund.de> wrote:
> Prof Brian Ripley wrote:
> > I get the second set each time, on Windows, using the build from CRAN.
> > Which BLAS are you using?
> 
> 
> Works also well for me with a self compiled R-1.9.1 (both with standard
> Rblas as well as with the Rblas.dll for Athlon CPU from CRAN).
> Is this a NT-based version of Windows (NT, 2k, XP)?
> 
> Uwe
> 
> 
> 
> 
> > On Tue, 14 Sep 2004, Francisco Chamu wrote:
> >
> >
> >>I start a clean session of R 1.9.1 on Windows and I run the following code:
> >>
> >>
> >>>library(MASS)
> >>>data(painters)
> >>>pca.painters <- princomp(painters[ ,1:4])
> >>>loadings(pca.painters)
> >>
> >>Loadings:
> >>            Comp.1 Comp.2 Comp.3 Comp.4
> >>Composition  0.484 -0.376  0.784 -0.101
> >>Drawing      0.424  0.187 -0.280 -0.841
> >>Colour      -0.381 -0.845 -0.211 -0.310
> >>Expression   0.664 -0.330 -0.513  0.432
> >>
> >>               Comp.1 Comp.2 Comp.3 Comp.4
> >>SS loadings      1.00   1.00   1.00   1.00
> >>Proportion Var   0.25   0.25   0.25   0.25
> >>Cumulative Var   0.25   0.50   0.75   1.00
> >>
> >>However, if I rerun the same analysis, the loadings of the first
> >>component have the opposite sign (see below), why is that?  I have
> >>read the note
> >>in the princomp help that says
> >>
> >>    "The signs of the columns of the loadings and scores are arbitrary,
> >>     and so may differ between different programs for PCA, and even
> >>     between different builds of R."
> >>
> >>However, I still would expect the same signs for two runs in the same session.
> >>
> >>
> >>>pca.painters <- princomp(painters[ ,1:4])
> >>>loadings(pca.painters)
> >>
> >>Loadings:
> >>            Comp.1 Comp.2 Comp.3 Comp.4
> >>Composition -0.484 -0.376  0.784 -0.101
> >>Drawing     -0.424  0.187 -0.280 -0.841
> >>Colour       0.381 -0.845 -0.211 -0.310
> >>Expression  -0.664 -0.330 -0.513  0.432
> >>
> >>               Comp.1 Comp.2 Comp.3 Comp.4
> >>SS loadings      1.00   1.00   1.00   1.00
> >>Proportion Var   0.25   0.25   0.25   0.25
> >>Cumulative Var   0.25   0.50   0.75   1.00
> >>
> >>>R.version
> >>
> >>         _
> >>platform i386-pc-mingw32
> >>arch     i386
> >>os       mingw32
> >>system   i386, mingw32
> >>status
> >>major    1
> >>minor    9.1
> >>year     2004
> >>month    06
> >>day      21
> >>language R
> >>
> >>BTW, I have tried the same in R 1.9.1 on Debian and I can't reproduce
> >>what I see
> >>on Windows.  In fact all the runs give the same as the second run on Windows.
> >>
> >>-Francisco
> >>
> >>______________________________________________
> >>R-help at stat.math.ethz.ch mailing list
> >>https://stat.ethz.ch/mailman/listinfo/r-help
> >>PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
> >>
> >>
> >
> >
> 
>