[R] Creating dummy variables in r

Bert Gunter gunter.berton at gene.com
Wed Jan 30 04:58:04 CET 2013

You almost never need dummy variables in R. R creates them
automatically from factors given model and possibly contrasts

?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:


I repeat: DO not create dummy variablesby hand in R unless you have
understood the above and have good reason to do so.

-- 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

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