Re: [R] rpart - the xval argument in rpart.control and in xpred.rpart
I have this *exact* same confusion. Adding to this is the fact that Everitt and Hothorn in their book, HSAUR, say that setting xval=100 gives "100 runs of 10-fold cross-validation" (1st ed., page 136). Is this actually 1 run of 100-fold cross-validation? For large xval, doing multiple cross-validations is not super important. But I would want to perform multiple cross-validataion with different partitions of the data when xval is moderate or small wrt the size of the data set. In that case do we need to do as Paolo suggests? Paolo Radaelli wrote: > > Usually 10-fold cross validation is performed more than once to get an > estimate of the misclassification rate thus I thought "number of > cross-validations" was different from the "number of cross-validation > groups". So, if I want to perform 10-fold cross-validation more than once > (say 5) in order to estimate the miscalssification rate I have to run > xpred.rpart 5 times ? > Thanks > Paolo > > >>> I have some problems in understanding the meaning of the xval argument >>> in >>> the two functions rpart.control and xpred.rpart. In the former it is >>> defined >>> as the number of cross-validations while in the latter it is defined as >>> the >>> number of cross-validation groups. >> It is the same thing. If xval=10 then the data is divided into 10 >> disjoint >> groups. A model is fit with group 1 left out and that model is used to >> predict >> the observations in group 1; then a model is fit with group 2 left out; >> then >> group 3, ... >> So 10 groups = 10 fits of the model. > > > > Actually I thought that in rpart.control > >> >> >> >> Terry Therneau >> >> > > __ > 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. > > -- View this message in context: http://www.nabble.com/Re%3A-rpart---the-xval-argument-in-rpart.control-and-in-xpred.rpart-tp23942907p25408496.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.
Re: [R] rpart - the xval argument in rpart.control and in xpred.rpart
Usually 10-fold cross validation is performed more than once to get an estimate of the misclassification rate thus I thought "number of cross-validations" was different from the "number of cross-validation groups". So, if I want to perform 10-fold cross-validation more than once (say 5) in order to estimate the miscalssification rate I have to run xpred.rpart 5 times ? Thanks Paolo I have some problems in understanding the meaning of the xval argument in the two functions rpart.control and xpred.rpart. In the former it is defined as the number of cross-validations while in the latter it is defined as the number of cross-validation groups. It is the same thing. If xval=10 then the data is divided into 10 disjoint groups. A model is fit with group 1 left out and that model is used to predict the observations in group 1; then a model is fit with group 2 left out; then group 3, ... So 10 groups = 10 fits of the model. Actually I thought that in rpart.control Terry Therneau __ 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.
Re: [R] rpart - the xval argument in rpart.control and in xpred.rpart
> I have some problems in understanding the meaning of the xval argument in > the two functions rpart.control and xpred.rpart. In the former it is defined > as the number of cross-validations while in the latter it is defined as the > number of cross-validation groups. It is the same thing. If xval=10 then the data is divided into 10 disjoint groups. A model is fit with group 1 left out and that model is used to predict the observations in group 1; then a model is fit with group 2 left out; then group 3, ... So 10 groups = 10 fits of the model. Terry Therneau __ 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.
[R] rpart - the xval argument in rpart.control and in xpred.rpart
Dear R users, I'm working with the rpart package and want to evaluate the performance of user defined split functions. I have some problems in understanding the meaning of the xval argument in the two functions rpart.control and xpred.rpart. In the former it is defined as the number of cross-validations while in the latter it is defined as the number of cross-validation groups. If I am correct this means that for xpred.rpart, xval denots the number V of one V-fold cross validation while for rpart.control it denotes the number of times that the cross-validation is performed. Am I right ? If so, how many subsets compose the learning sample when performing one of the xval cross-validations ? Is it a 10-fold cross-validation repeated xval=10 times ? Thank you for your help Paolo Paolo Radaelli Dipartimento di Metodi Quantitativi per le Scienze Economiche ed Aziendali Facoltà di Economia Università degli Studi di Milano-Bicocca Via Bicocca degli Arcimboldi, 8 20126 Milano Italy e-mail paolo.radae...@unimib.it Tel +39 02 6448 3163 Fax +39 02 6448 3105 __ 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.
