[R] replacing characters in formulae / models

[Charles C. Berry]

On Thu, 6 Nov 2008, Christoph Scherber wrote:

> Dear all,
>
> How can I replace text in objects that are of class "formula"?
>
> y="a * x + b"
> class(y)="formula"
> grep("x",y)
> y[1]


What exactly are you trying to accomplish??

And why did you assign 'formula' as the class of a character string?

'y' is not a valid formula object:

> lm(y)
Error in terms.formula(formula, data = data) :
   argument is not a valid model

=====

Perhaps, you need to review

 	?formula

and
 	11 Statistical models in R

from Introduction to R.

Oh, yes. There is the matter of reviewing the _posting guide_ before 
posting, too.

HTH,

Chuck


>
> Suppose I would like to replace the "x" by "w" in the formula object "y".
>
> How can this be done? Somehow, the methods that can be used in character 
> objects do not work 1:1 in formula objects...
>
> Many thanks and best wishes
> Christoph
>
>
>
> -- 
> Dr. rer.nat. Christoph Scherber
> University of Goettingen
> DNPW, Agroecology
> Waldweg 26
> D-37073 Goettingen
> Germany
>
> phone +49 (0)551 39 8807
> fax   +49 (0)551 39 8806
>
> Homepage http://www.gwdg.de/~cscherb1
>
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901