On Tue, 2005-11-22 at 08:53 -0400, Roy Little wrote: > Dear list, > I have a question concerning the above mentioned methods in the pls > package with respect to the loadings matrix produced by the call. In > some work I am doing I have found that the values produced are nearly of > the same magnitude but of opposite sign. When I use the example data > (sensory) I find this result reproduced. I am prepared to work this > through but I have a feeling that there could be a possible error in the > code. (?!)
But only for the first axis! I am not an expert, but as I understand it, PCR and PLS are related but different methods. PCR components maximise variance within the predictor variables, whilst PLS components maximise the covariance with the response variable. Both methods appear to extract first components that are similar - perhaps indicative of strong structure within the data set. That the subsequent components are different reflects the different criteria maximised by the two methods. Prof. Ripley has indicated where to look for discussions about the signs of eigenvectors. Maybe I misunderstood your query? Were you expecting the results to be the same on all components? Why do you suspect an error in the code? HTH, Gav > > > > sens.pcr$loadings > Comp 1 Comp 2 Comp 3 Comp 4 > yellow 75.186621 -0.4780473 3.212149 1.750123 > green -90.490256 8.5880530 1.634961 1.042239 > brown -2.861241 -11.3600509 -15.920789 -1.105799 > glossy 13.347090 19.3103902 -3.121693 2.781282 > transp 20.126987 24.0653312 -6.656764 -1.842907 > syrup -7.199972 -5.3436196 -5.073675 5.620454 > > sens.pls$loadings > > Loadings: > Comp 1 Comp 2 Comp 3 Comp 4 > yellow -74.448 -10.519 3.169 -1.056 > green 88.299 21.627 -0.521 -0.976 > brown 4.959 -14.253 -12.761 -0.371 > glossy -15.798 15.914 -7.574 3.504 > transp -23.049 18.673 -12.214 -2.068 > syrup 8.045 -5.313 -3.698 2.181 > > Thank you for your help. > > Roy Little > Dept. Chem. > Facultad de Ciencias > Universidad de los Andes > Mérida, Venezuela > > ______________________________________________ > [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 -- %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% Gavin Simpson [T] +44 (0)20 7679 5522 ENSIS Research Fellow [F] +44 (0)20 7679 7565 ENSIS Ltd. & ECRC [E] gavin.simpsonATNOSPAMucl.ac.uk UCL Department of Geography [W] http://www.ucl.ac.uk/~ucfagls/cv/ 26 Bedford Way [W] http://www.ucl.ac.uk/~ucfagls/ London. WC1H 0AP. %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% ______________________________________________ [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
