[R] how to fix a factor

[Vaclav Petricek]

On Fri, 19 Mar 2004, Giampiero Salvi wrote:

> Hi all,
> 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)
>
> for example I'd like to write something like
>
> boxplot(y ~ x1 + x2, x3 == 1)
>
> which of course doesn't work, otherwise I wouldn't write :-)
>
> Is this possible and how?

?boxplot

The subset parameter of boxplot might be what you are looking for.

Vaclav