Liaw, Andy
2004-Nov-15 18:24 UTC
[R] how to obtain predicted labels for test data using "kerne lpls"
You need to do some extra work if you want to do classification with a regression method. One simple way to do classification with PLS is to code the classes as 0s and 1s (assuming there are only two classes) or -1s and 1s, fit the model, then threshold the prediction; e.g., those with predicted values < 0.5 (in the 0/1 coding) get labeled as 0s. There's a predict() method for mvr objects, and that's what you need to use to get prediction on test set. There's one more complication: The CV done internal to mvr is optimizing the MSE (because it rightly thinks it has a regression problem), but that will almost certainly not be the thing to do for classification. You have two choices: Do your own CV, or modify code in pls.pcr to do the "right" CV when given classification data. You might want to look at the `gpls' package, which started out as part of BioConductor, then was made available on CRAN, but now seem to have move back to BioConductor. It treats classification problems in a more `natural' way. HTH, Andy> From: Huh, Seungho > > Dear members, > > My name is Seungho Huh. I am a statistician who tries to use > the Kernel > PLS method in a classification problem. I am sending this email to ask > you something about the "kernelpls" function in R (pls.pcr package). > > I would like to obtain the predicted Y values for test data, using the > Kernel PLS method. Let's take the example in the R help: > > > data(NIR) > > attach(NIR) > > NIR.kernelpls <- mvr(Xtrain, Ytrain, 1:6, validation = "CV", > method="kernelPLS") > > > > How can we get the predicted Y values ("Ypred") for Xtest in > this case? > As far as I checked, there is no parameter to specify the test data in > "mvr" or "pls". I, therefore, thought about the "kernelpls" > function as > follows: > > > > > Kernelpls(Xtrain, Ytrain, ncomp = 21, Xtest) > > > > Is this the correct way of getting Ypred for Xtest? I am > afraid that it > says in the help of "kernelpls", "this function should not be called > directly, but through the generic pls function with the argument > method="kernel" (default)." I would really appreciate it if > you can give > some advice on this. > > > > Thanks a lot for your time. > > > > Seungho Huh, Ph.D. > > Research Statistician > > RTI International > > North Carolina, USA > > > > > > > [[alternative HTML version deleted]] > > ______________________________________________ > 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 > >
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