On Jan 30, 2013, at 04:58 , Bert Gunter wrote: > You almost never need dummy variables in R. R creates them > automatically from factors given model and possibly contrasts > specification. > > ?contrasts ## for some technical details. > > If you have not read "An Introduction to R" do so now. Pay particular > attention to the chapter on modeling and categorical variables. You > can also google around to find appropriate tutorials. Here is one: > > http://www.ats.ucla.edu/stat/r/modules/dummy_vars.htm > > I repeat: DO not create dummy variablesby hand in R unless you have > understood the above and have good reason to do so.
In this case it's a cutpoint-type situation, and the user might be excused for not wanting to deal with the mysteries of cut() (yet). More importantly, the main issue here seems to be a lack of understanding of where new variables are located. I.e., if the data set is called dd, you need dd$prev1 <- (etc) and if you use attach(), do it _after_ modifying the data (or detach() and reattach). Otherwise, new variables end up in the global environment. (This is logical enough once you realize that the result of a computation does not necessarily "fit" into the dataset.) By the way: You don't need ifelse(): as.numeric(ret1 >= .5) or even just (ret1 >= .5) works. > > -- Bert > > On Tue, Jan 29, 2013 at 7:21 PM, Joseph Norman Thomson > <thoms...@email.arizona.edu> wrote: >> Hello, >> >> Semi-new r user here and still learning the ropes. I am creating dummy >> variables for a dataset on stock prices in r. One dummy variable is >> called prev1 and is: >> >> prev1 <- ifelse(ret1 >= .5, 1, 0) >> >> where ret1 is the previous day's return. >> >> The variable "prev1" is created fine and works in my regression model >> and for running conditional statistics. However, when I call the >> names() function on the dataset the freshly created variable (prev1) >> doesn't show up; also, when I export the dataset the prev1 variable >> doesn't show up in the exported file. Is there a way to make the >> variable show up on both the call function but more importantly on the >> exported file? Or am I forced to create dummy variables elsewhere(much >> tougher)? >> >> >> Thanks, >> >> Joe >> >> ______________________________________________ >> 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. -- Peter Dalgaard, Professor Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Email: pd....@cbs.dk Priv: pda...@gmail.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.
