[R-sig-ME] GLS, as.formula and subsitute

[Sven Hohenstein]

Dear Christoph,

(1) The function substitute is used for expressions, not for formulas.  
You can dynamically create a formula with the reformulate function:

reformulate("Time", resp)

The first argument denotes the right-hand side of the formula, the  
second argument denotes the response.

(2) In your example, DF refers to the string "Ovary". This is not the  
same as the object named Ovary. To access an object by its name  
string, the function get can be used.

The complete code:

##
library(nlme) # for gls()

models <- function(resp = resp, DF = DF) {
   f1 <- reformulate("Time", resp)
   gls(f1, data = get(DF))
}

models(resp = "follicles", DF = "Ovary")
##

Best,
Sven


Quoting Christoph Scherber <christoph.scherber at agr.uni-goettingen.de>:

> Dear all,
>
> I am trying to feed a formula object into GLS using substitute() and  
>  as.formula(). What am I doing
> wrong here?
>
> ##
> models <- function(resp=quote(resp),DF=quote(DF)) {
> f1=substitute(resp~Time,list(resp=quote(resp)))
> gls(as.formula(f1),data=DF)
> }
>
> models(resp="follicles","Ovary")
>
> ##
> Many thanks for your help!
>
> Best wishes
> Christoph
>
> --
> PD Dr Christoph Scherber
> Georg-August University Goettingen
> Department of Crop Science
> Agroecology
> Grisebachstrasse 6
> D-37077 Goettingen
> Germany
> phone 0049 (0)551 39 8807
> fax 0049 (0)551 39 8806
> http://www.gwdg.de/~cscherb1
>

-- 
Sven Hohenstein
Department of Psychology
University of Potsdam
Karl-Liebknecht-Str. 24-25
14476 Potsdam
Germany
Tel.: ++49 331-977 2370