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 ______________________________________________ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html