[R] how calculate mean for each group

[kjetil brinchmann halvorsen]

On 2 Oct 2003 at 16:11, Simon Fear wrote:

> 
> (BTW did I ever mention here how much I prefer with() to 
> attach()/forget.to.detach() ?)
> 
 Agreed. I learnt about with() a few weeks ago and hasn't used 
attach()/forget to detach() since. 

Kjetil Halvorsen