Noah, depending on what function you use, it might do this automatically for you if you give the function a formula containing a factor. Otherwise, see ?model.matrix.
-----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Noah Silverman Sent: Wednesday, August 12, 2009 3:59 PM Cc: r help Subject: Re: [R] Nominal variables in SVM? That makes sense. I my data is already nominal, I need to "expand" a single column into several binary ones. Is there an easy function to do this in R, or do I need to create something from scratch? (If I have to create my own, any suggestions?) Thanks! -N On 8/12/09 1:55 PM, Steve Lianoglou wrote: > Hi, > > On Aug 12, 2009, at 2:53 PM, Noah Silverman wrote: > >> Hi, >> >> The answers to my previous question about nominal variables has lead >> me to a more important question. >> >> What is the "best practice" way to feed nominal variable to an SVM. >> >> For example: >> color = ("red, "blue", "green") >> >> I could translate that into an index so I wind up with >> color= (1,2,3) >> >> But my concern is that the SVM will now think that the values are >> numeric in "range" and not discrete conditions. >> >> Another thought would be to create 3 binary variables from the single >> color variable, so I have: >> >> red = (0,1) >> blue = (0,1) >> green = (0,1) >> >> A example fed to the SVM would have one positive and two negative >> values to indicate the color value: >> i.e. for a blue example: >> red = 0, blue =1 , green = 0 > > Do it this way. > > So, imagine if the features for your examples were color and height, > your "feature matrix" for N examples would be N x 4 > > 0,1,0,15 # blue object, height 15 > 1,0,0,10 # red object, height 10 > 0,0,1,5 # green object, height 5 > ... > > -steve > > -- > Steve Lianoglou > Graduate Student: Computational Systems Biology > | Memorial Sloan-Kettering Cancer Center > | Weill Medical College of Cornell University > Contact Info: http://cbio.mskcc.org/~lianos/contact > ______________________________________________ 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-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.
