[R] Converting a categorical variable to multiple dichotemousvariables

[Shane Phillips]

Here is my original script.  

subject=1:1000
treat=rbinom(1*1000,1,.13)
gender=rbinom(1*1000,1,.5)
eth=runif(1*1000, min=1, max=4)
cogat=rnorm(1*1000, 100, 16)
map=rnorm(1*1000, 200, 9)
growth=0
simtest=data.frame (subject=subject, treat=treat, gender=gender, eth=round(eth,digits=0), cogat=round(cogat,digits=0),map=round(map,digits=0),growth)
simtest<-transform(simtest, growth=rnorm(1000,m=ifelse(treat==0,0.1,0.5),s=0.03))
simtest

The categorical variable I'm looking at is "eth."  I want to change it to a factor.  The code you gave works great by itself, but I can't apply it to this program.

Sorry!  I'm really new to this.

Thanks for your help!
Shane



-----Original Message-----
From: Dr. Pablo E. Verde [mailto:PabloEmilio.Verde at uni-duesseldorf.de] 
Sent: Tuesday, April 12, 2011 8:53 AM
To: andrija djurovic; Shane Phillips
Cc: r-help at r-project.org
Subject: Re: [R] Converting a categorical variable to multiple dichotemousvariables

Hi Shane,

An alternative is:

cat<-as.factor(c(1,1,3,2,4))
outer(cat, levels(cat), "==")+0

Cheers,

Pablo


----- Original Message ----- 
From: "andrija djurovic" <djandrija at gmail.com>
To: "Shane Phillips" <SPhillips at lexington1.net>
Cc: <r-help at r-project.org>
Sent: Tuesday, April 12, 2011 2:32 PM
Subject: Re: [R] Converting a categorical variable to multiple 
dichotemousvariables


> hi:
> here is one solution:
>
> cat<-as.factor(c(1,1,3,2,4))
> model.matrix(~cat-1,cat)
>
> cbind(cat,model.matrix(~cat-1,cat))
> Andrija
>
> On Tue, Apr 12, 2011 at 2:17 PM, Shane Phillips 
> <SPhillips at lexington1.net>wrote:
>
>> I have a categorical variable in a dataframe similar to the following...
>>
>> cat
>> 1
>> 1
>> 3
>> 2
>> 4
>>
>> I need to convert it to 4 dichotemous variables for each observations
>> like...
>>
>> cat1    cat2    cat3    cat4
>> 1       0       0       0
>> 1       0       0       0
>> 0       0       1       0
>> 0       1       0       0
>> 0       0       0       1
>>
>>
>> Thanks in advance!
>>
>> Shane
>>
>> ______________________________________________
>> 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<http://www.r-project.org/posting-guide.html>
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> 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.
>