[R] Combining Factors in model.matrix

[paul.boutros@utoronto.ca]

Hello,

I want to be able to create a design matrix with two factors.  For instance, if 
I have:

> t1 <- factor(c(1,1,2,2));
> t2 <- factor(c(1,2,1,2));
> design <- model.matrix(~ -1 + (t1+t2));
> design;
  t11 t12 t22
1   1   0   0
2   1   0   1
3   0   1   0
4   0   1   1

But the design matrix I want is:
   t1 t2
1   1  0
2   1  1
3   0  0
4   0  1

Actually, in general I'm struggling with the syntax for formulating a design 
matrix I can write down on paper.  Is there a reference for this beyond the R 
documentation?

Thanks,
Paul