Martin,
If the data are actually coded 0/1, the tree function would
probably intepret them as integers and try a regression instead of a
classification. If the dependent variable is called "var", try
x <- tree(factor(var)~species)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
David W. Roberts office 406-994-4548
Professor and Head FAX 406-994-3190
Department of Ecology email [EMAIL PROTECTED]
Montana State University
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Martin Wegmann wrote:
> Dear R-user,
>
> I tried to generate classification / regression tree with a absence/presence
> matrix of species (400) in different locations (50) to visualise species
> which are important for splitting up two locations.
> Rpart and tree did not work for more than 10 species which is logical due to
> the limited amount of locations (n=50). However the error prompt is a "+" and
> no specific message, but I am pretty sure that I did not enter a false sign
> by mistake.
> Is it allowed at all to use 0/1 data for this statistical technique and if
> yes
> is there a way or different method to use all 400 species entries?
> Otherwise I would apply a PCA beforehand but I would prefer to have the raw
> species informations.
>
> using R 2.1.1-1 (debian repos.)
>
> regards, Martin
>
>
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