[R] Specification of model formulae

[kjetil@entelnet.bo]

On 16 Apr 2004 at 17:08, Christian Hennig wrote:

You can build your formula along the ways of the following example, 
without typing the 200 names:

> nam <- paste("var", 1:5, sep="", collapse="+")
> nam
[1] "var1+var2+var3+var4+var5"
> nam <- paste("y", nam, sep="~")
> nam
[1] "y~var1+var2+var3+var4+var5"
> as.formula(nam)
y ~ var1 + var2 + var3 + var4 + var5

Kjetil Halvorsen

> Hi,
> 
> is it true that the only way to tell rpart which variables to use is
> to specify every single variable in the formula and separate them with
> "+"?
> 
> I wonder if this error...
> 
> > rotree <- rpart(powerdata[,1]~powerdata[,2:3],
> +                      method="class")
> Error in model.frame(formula, rownames, variables, varnames, extras,
> extranames,  : 
>  invalid variable type
> 
> ...can be prevented by other means than...
> 
> > rotree <- rpart(segments~V1.3+V1.9,
> +                      method="class",data=powerdata)
> 
> This works.
> (The variables here are powerdata[,1] and [,2:3].)
> 
> But I do not want to write 200 variable names down, as this is the
> real size of "powerdata".
> 
> Is there any way around that?
> 
> Christian
> 
> 
> 
> **********************************************************************
> * Christian Hennig Fachbereich Mathematik-SPST/ZMS, Universitaet
> Hamburg hennig at math.uni-hamburg.de,
> http://www.math.uni-hamburg.de/home/hennig/
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