[R] Problem with terms of the form (a >1) and subsetting of a terms object

[Dimitris Rizopoulos]

I think you need an I(), i.e.,

form <- ~ I(a > 1) - 1


I hope it helps.

Best,
Dimitris


On 8/26/2010 9:17 AM, Niels Richard Hansen wrote:
> I have the following problem
>
> mydata <- data.frame(a=1:3)
> form <- ~ (a>1) - 1
> model.matrix(form,mydata)
>
> a > 1FALSE a > 1TRUE
> 1 1 0
> 2 0 1
> 3 0 1
> ...
>
> However
>
> model.matrix(update(terms(form)[1],~.-1),mydata)
>
> (Intercept) a > 1 - 1TRUE
> 1 1 1
> 2 1 1
> 3 1 1
> ...
>
> Taking
>
> terms(form)[1]
>
> extracts the formula with only the first term, but the parentheses
> are thrown away, and after the update, I get a different formula.
> Is that supposed to be so?
>
> Thanks, Niels
>

-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

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