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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