[R] factors ordered by mean

[Ronaldo Reis Junior]

Hi,

How to order the levels os factor not by alphabetic order but by mean of Y. 
Somethink like this:

I have this alphabetic order:

> levels(pH)
[1] "alto"  "baixo" "medio"

the order by mean os yvar is:
> sort(tapply(Riqueza,pH,mean))
   baixo    medio     alto 
11.56667 20.00000 26.80000 

How to make the levels of pH ordered by this mean to the result to see 
somethink like this:

> levels(pH)
[1] "baixo"  "medio"  "alto"

I try this to make a function that I need to get ordered levels by this mean 
and after rename to make a automatic contrasts by comparing models.

> levels(pH)[1] <- "baixomedio"
> levels(pH)[2] <- "baixomedio"
> levels(pH)
[1] "baixomedio"  "alto"

and after this a make a new model to be compared with a model with 3 levels 
where "baixo" and "medio" is separated.

without ordered levels these command is wrong because the levels(pH)[1] 
is "alto" and not "baixo". 

Normally I use recode from car package, but for automatization your syntax is 
a difficult.

Thanks
Ronaldo
--
> Prof. Ronaldo Reis Júnior
|  .''`. UNIMONTES/Depto. Biologia Geral/Lab. de Biologia Computacional
| : :'  : Campus Universitário Prof. Darcy Ribeiro, Vila Mauricéia
| `. `'` CP: 126, CEP: 39401-089, Montes Claros - MG - Brasil
|   `- Fone: (38) 3229-8187 | ronaldo.reis em unimontes.br | chrysopa em gmail.com
| http://www.ppgcb.unimontes.br/ | ICQ#: 5692561 | LinuxUser#: 205366