To all who ask about dummy variables in R: Please please read the "Introduction to R" section on "Statistical Models in R" or other tutorial (there are many on the web) on regression modeling in R. (For that matter -- please read all of this or other basic R tutorial before posting here!). An excellent but somewhat terse and technical discussion can be found in the latest edition of V&R's MASS -- the chapter on linear models. I do not intend to (poorly) try to recapitulate what others have already (well) explained. Do Your Homework!
Documentation within R can be found in ?lm ?formula ?contrasts ?model.matrix These may not make much sense unless you have done your homework first -- or already understand the statistical issues. -- Bert On Sat, Apr 20, 2013 at 3:56 PM, Eva Prieto Castro <evapcas...@yahoo.es>wrote: > > Hi, > > Why do you write that dummy variables are not needed in R?. I would like > you explain it. > > Thanks, > > Eva > > --- El *dom, 21/4/13, David Winsemius <dwinsem...@comcast.net>* escribió: > > > De: David Winsemius <dwinsem...@comcast.net> > Asunto: Re: [R] creating dummy variables > Para: "Bert Gunter" <gunter.ber...@gene.com> > CC: "r-help@R-project.org" <r-help@r-project.org>, "shyam basnet" < > shyamabc2...@yahoo.com> > Fecha: domingo, 21 de abril, 2013 00:38 > > > On Apr 20, 2013, at 2:03 PM, Bert Gunter wrote: > > > Dummy variables are not needed in R. > > > > Bert > > > > Bert is correct on this point, but if you what to know how the regression > functions in R do this "behind the scenes" then you could always look at: > > ?model.matrix # where _some_ of the the automagical stuff happens > > > model.matrix( ~ crop, data=dat[,"crop", drop=FALSE]) > (Intercept) cropSWHE > 1 1 1 > 2 1 1 > 3 1 0 > 4 1 0 > 5 1 1 > 6 1 1 > 7 1 0 > 8 1 0 > attr(,"assign") > [1] 0 1 > attr(,"contrasts") > attr(,"contrasts")$crop > [1] "contr.treatment" > > > > > Sent from my iPhone -- please excuse typos. > > > > On Apr 20, 2013, at 11:23 AM, shyam basnet > > <shyamabc2...@yahoo.com<http://mc/compose?to=shyamabc2...@yahoo.com>> > wrote: > > > >> Hello R-users, > >> > >> The below is a snippet of my data: > >> > >> > >> fid crop year value > >> 5_1_1 SWHE 1995 171 > >> 5_1_1 SWHE 1997 696 > >> 5_1_1 BARL 1996 114 > >> 5_1_1 BARL 1997 344 > >> 5_2_2 SWHE 1995 120 > >> 5_2_2 SWHE 1996 511 > >> 5_2_2 BARL 1996 239 > >> 5_2_2 BARL 1997 349 > >> > >> Here, I want to create dummy variables with the names of the content of > a column 'crop' in a way that the new variable 'SWHE' would receive a value > of 1 if the column 'crop' contains 'SWHE' and 0 otherwise. So, I would have > two new variables SWHE and BARL as below: > >> > >> > >> fid crop year value SWHE BARL > >> 5_1_1 SWHE 1995 171 1 0 > >> 5_1_1 SWHE 1997 696 1 0 > >> 5_1_1 BARL 1996 114 0 1 > >> 5_1_1 BARL 1997 344 0 1 > >> 5_2_2 SWHE 1995 120 1 0 > >> 5_2_2 SWHE 1996 511 1 0 > >> 5_2_2 BARL 1996 239 0 1 > >> 5_2_2 BARL 1997 349 0 1 > >> > >> > >> Cheers, > >> Shyam > >> Nepal > >> > > David Winsemius > Alameda, CA, USA > > ______________________________________________ > R-help@r-project.org <http://mc/compose?to=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 [[alternative HTML version deleted]]
______________________________________________ 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.
