[Rd] calculating means per group

[Prof Brian Ripley]

On Thu, 4 Sep 2008, ONKELINX, Thierry wrote:

> Dear Luc,
>
> You should send this kind of questions to the general mailing list
> (r-help at r-project.org) instead of the developer list.
>
> To answer your question: have a look at ?by and ?aggregate

And ?ave .

> HTH,
>
> Thierry

> -----Oorspronkelijk bericht-----
> Van: r-devel-bounces at r-project.org
> [mailto:r-devel-bounces at r-project.org] Namens RFTW
> Verzonden: donderdag 4 september 2008 9:07
> Aan: r-devel at r-project.org
> Onderwerp: [Rd] calculating means per group
>
>
> Hi all
> I have a very basic question, yet i have not found how to do it.
>
> Suppose my dataset looks like this:
>
> Year	Area	value
> 1	a	20
> 1	a	25
> 1	a	28
> 1	a	31
> 1	a	23
> 1	b	25
> 1	b	28
> 1	b	23
> 1	b	19
> 2	a	25
> 2	a	23
> 2	a	24
> 2	a	26
> 2	b	27
> 2	b	28
> 2	b	20
> 2	b	25
> 2	b	28
>
>
> Now, i want to calculate a MEAN per year per area. How do i do that?
>
> With mean(value) i calculate the mean of all values of course. I just
> need
> to know how to group year and area correctly.
>
> I assume that i can use this grouping in other calculations too, right?
>
>
> Cheers,
>
> Luc
> -- 
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> ml
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>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595