[R] Using "mean" if two values are identical

[Julien Barnier]

Hi,

> I've got a matrix (mail end) with the colnames x, y, z. In this matrix
> are different measurements. x and y are risign coordinates.
>
> My question. Always, if the "x" AND "y" coordinates are the same, I want to 
> get the mean of their z values.

Maybe you could try with the aggregate function, for example  :

aggregate(INPUT[,3], by=list(INPUT[,1],INPUT[,2]), FUN=mean)

Hope that helps,
-- 
Julien Barnier
Groupe de recherche sur la socialisation
ENS-LSH - Lyon, France