[R] Efficiently create dummy

[Dimitris Rizopoulos]

well, you can first define a factor, and the use model.matrix(), e.g.,

fc <- factor(c("AR", "DE", "MS", "NY"))
model.matrix(~ fc)


for more info check ?model.matrix(), e.g., if you want to change the 
contrasts.

I hope it helps.

Best,
Dimitris


Rob Denniker wrote:
> What's the neat way to create a dummy from a list?
> The code below is not replicable, but hopefully self-explanatory...
> 
> d$treatment<-rep(1,length(d))
> 
> notreat<-c("AR", "DE", "MS", "NY", "TN", "AK", "LA", "MD",  "NC", "OK", "UT", "VA")
> 
> #i would really like this to work:
> d$treatment[d$st==any(notreat)]<-0
> 
> #but instead i resort to this
> for (i in 1:length(notreat)) {
> temp.st <- notreat[i]
> d$treatment[d$st==temp.st]<-0
> i<-i+1 }
> 
> 
> Thanks, list!
> 
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-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

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