Creating dummy variables in r
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 <thomsonj at 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
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-- 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
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