R help - Jan 2013 - Creating dummy variables in r

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

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.

-- 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
>
> ______________________________________________
> R-help at 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