Coding categorical -> dummy

Dear R-Users,

I have a data frame with several categorical variables. I want to code
these variables in dummy variables keeping all levels.
I know the function model.matrix (see below) but it works only for one
categorical variable :

tt <- c("a","a","b","a","c")
tt <- factor(tt)
model.matrix(~ tt - 1)

Is there anyone who have write such function ?
Thanks for your help.

Samir Messad


Samir Messad    E-Mail : messad at cirad.fr
Statisticien
CIRAD-EMVT
TA 30/A
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Campus de Baillarguet
34398 Montpellier cedex 5 (France)

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