On 26/08/10 09.30, Dimitris Rizopoulos wrote:
I think you need an I(), i.e.,
form <- ~ I(a > 1) - 1
Yes, it solves the concrete problem, but does not really answer
the question. Let me rephrase. Should the use of terms like (a>1)
be discouraged in R and replaced by I(a>1) systematically, or is the
behavior below unexpected?
Best, Niels
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
--
Niels Richard Hansen Web: www.math.ku.dk/~richard
Associate Professor Email: niels.r.han...@math.ku.dk
Department of Mathematical Sciences nielsrichardhan...@gmail.com
University of Copenhagen Skype: nielsrichardhansen.dk
Universitetsparken 5 Phone: +45 353 20783 (office)
2100 Copenhagen Ø +45 2859 0765 (mobile)
Denmark
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