try tapply() if you want the values for all levels of x, or calculate your
mean after a subset()

Check the documentation on both of these.

Mike

On Wed, Dec 8, 2010 at 9:54 AM, madr <madrazel@interia.pl> wrote:

>
> for example I have matrix with two columns
>
> x,y
> 1,0.56
> 2,9.55
> 2,7.56
> 5,2.55
> 5,0.56
> 3,0.55
> 2,0.56
> 2,1.56
>
> so I need to take average from y values placed where x==2
> --
> View this message in context:
> http://r.789695.n4.nabble.com/how-to-make-partial-mean-of-a-matrix-only-when-second-value-matching-some-logic-tp3078449p3078449.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help@r-project.org mailing list
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html>
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Michael Rennie, Research Scientist
Fisheries and Oceans Canada, Freshwater Institute
Winnipeg, Manitoba, CANADA

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