[R] CART for 0/1 data

[Dave Roberts]

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 droberts at montana.edu
Montana State University
Bozeman, MT 59717-3460


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
> 
>