... and adding to what has already been said, PCA can be distorted by non-ellipsoidal distributions or small numbers of unusual values. Careful (chiefly graphical) examination of results is therefore essential, and usually fairly easy to do. There are robust/resistant versions of PCA in R, but they come with their own issues. As you have already been told, you need to do some homework -- or get some local advice.
Also, you need to post on some other list, e.g. stats.stackexchange.com, as you have wandered outside the realm of R issues. -- Bert On Sat, Dec 10, 2011 at 10:40 AM, Mark Difford <mark_diff...@yahoo.co.uk> wrote: > On Dec 10, 2011 at 5:56pm deb wrote: > >> My question is, is there any way I can map the PC1, PC2, PC3 to the >> original conditions, >> so that i can still have a reference to original condition labels after >> PCA? > > deb, > > To add to what Stephen has said. Best to do read up on principal component > analysis. Briefly, each PCA is composite variable, composed of different > "amounts" of each and every one of your column variables, i.e. cond1, ..., > cond1000. > > So the short answer to your question is no. There is no way to do this > mapping, except as loadings on each principal component (PC). > > Regards, Mark. > > ----- > Mark Difford (Ph.D.) > Research Associate > Botany Department > Nelson Mandela Metropolitan University > Port Elizabeth, South Africa > -- > View this message in context: > http://r.789695.n4.nabble.com/PCA-on-high-dimentional-data-tp4180467p4180890.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. -- Bert Gunter Genentech Nonclinical Biostatistics Internal Contact Info: Phone: 467-7374 Website: http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
