That did it! Thanks Marc.
- Christian
On 11/15/06, Marc Schwartz <[EMAIL PROTECTED]> wrote:
>
> On Wed, 2006-11-15 at 15:03 -0500, Christian Convey wrote:
> > Thanks, let me try to clarify my question with an example.
> >
> > Suppose I have the following data:
> >
> > Gender, Major, Course-Grade
> > F, Psy, 3.5
> > F, Psy, 3.1
> > M, Hst, 3.7
> > F, Hst, 3.6
> > M, Hst, 2.6
> > M, Eng, 3.9
> >
> > I want to compute a table like the following:
> >
> > X-axis: Gender
> > Y-axis: Major
> > Cell(x,y) = mean course-grade
> >
> > So for example, with the data above:
> >
> > F M
> > ------------------------
> > Psy | 3.3 NA
> > Hst | 3.6 3.15
> > Eng | NA 3.9
> >
> > If I were doing this in SQL I'd do it with a cross-tab query. But the
> world
> > of R still has much unfamiliar terrain :)
> >
> > Thanks,
> > Christian
>
>
> Presuming that DF is a data frame containing your data:
>
> > with(DF, tapply(Course.Grade, list(Major, Gender),
> mean, na.rm = TRUE))
> F M
> Eng NA 3.90
> Hst 3.6 3.15
> Psy 3.3 NA
>
>
> See ?tapply and ?with
>
> HTH,
>
> Marc Schwartz
>
>
>
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