[R] how to fix a factor

[Chuck Cleland]

Giampiero Salvi wrote:
> I created a data frame with three factors, plus the response that
> looks like this:
> 
> x1	x2	x3	y
> a	1	1	0.3
> a	2	1	0.1
> b	1	1	0.4
> c	4	3	0.1
> ...
> 
> I would like to analise the effect of two of them, keeping the third fixed
> (I already know the effect of the last). The reason why I don't create several
> data frames for each value of the thirs factor is simply convenience (I'd like
> to be able to decide which factor I want to rule out)

boxplot(y ~ x1 + x2, data = mydata[mydata$x3==1,])

-- 
Chuck Cleland, Ph.D.
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