[R] linear model coefficients

Joerg Schaber Joerg.Schaber at uv.es
Mon Jul 28 17:36:12 CEST 2003


I wonder if there is a possibility to avoid that R sets one level of a 
factor equal zero in a model fit.

More precisely, I want to fit a two-way unbalanced linear model: o ~ 0 + 
x + y
x is a factor with 10 levels, y is a factor with 9 levels. In order to 
get a unique solution
i set the intercept =0 and impose that sum(y)=0 i.e.
res <- lm(o ~ 0 + x + y, contrasts=list(y=("contr.sum")))

However, R keeps returning only 8 coefficients for y. I assume that 
internally one coefficient is always set to zero. But when I impose 
"contr.sum", setting one coef to zero is no longer really nessasary, 
isn't it?

So my questions is, if there is a way yo avoid that, or am I completely 



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