Re: [R] logistic regression and dummy variable coding

From: Bingshan Li <bli1_at_bcm.tmc.edu>
Date: Thu, 28 Jun 2007 20:00:23 -0500

Hi All,

Now it works. Thanks for all your answers and the explanations are very clear.

Bingshan

On Jun 28, 2007, at 7:44 PM, Seyed Reza Jafarzadeh wrote:

> NewVar <- relevel( factor(OldVar), ref = "b")
> should create a dummy variable, and change the reference category
> for the model.
>
> Reza
>
>
> On 6/28/07, Bingshan Li <bli1_at_bcm.tmc.edu> wrote:
>> Hello everyone,
>>
>> I have a variable with several categories and I want to convert this
>> into dummy variables and do logistic regression on it. I used
>> model.matrix to create dummy variables but it always picked the
>> smallest one as the reference. For example,
>>
>> model.matrix(~.,data=as.data.frame(letters[1:5]))
>>
>> will code 'a' as '0 0 0 0'. But I want to code another category as
>> reference, say 'b'. How to do it in R using model.matrix? Is there
>> other way to do it if model.matrix has no such functionality?
>>
>> Thanks!
>>
>>
>>
>> [[alternative HTML version deleted]]
>>
>> ______________________________________________
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>> guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>



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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. Received on Fri 29 Jun 2007 - 01:05:53 GMT

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