[R] Specification of model formulae

[Uwe Ligges]

Christian Hennig wrote:
> 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

Consider to use

rotree <- rpart(segments ~ ., method = "class", data = powerdata)

The "." defines all variables in powerdata, except for "segments", as 
usual for formulas.

Uwe Ligges





> 
> 
> ***********************************************************************
> 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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