[R] newbie question about index

[Gabor Grothendieck]

Here is an additional way:

model.matrix(~ factor(a) - 1)


On 9/1/06, Gabor Grothendieck <ggrothendieck at gmail.com> wrote:
> Try using outer:
>
> outer(1:3, a, "==")+0
>
>
>
>
> On 8/31/06, z s <flyhyena at yahoo.com.cn> wrote:
> > Hi,
> >
> >  I am trying to convert a variable a = sample(1:3,100,rep = T) represents choices into a 3X100 dummy varible b with corresponding element set to 1 otherwise 0.
> > eg.
> >
> > a: 1 3 2 1 2 3 1 1....
> >
> > b: 1 0 0 1 0 0 1 1..
> >    0 0 1 0 1 0 0 0...
> >    0 1 0 0 0 1 0 0...
> >
> >  Is there something like b[a] =1 existing? I could not figure this out myself.
> >
> >
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