[R] CART for 0/1 data

[Martin Wegmann]

On Friday 23 September 2005 17:08, Dave Roberts wrote:
> 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

thanks, but I think I provided too less informations. 
My dependent variable are the locations which are names (I could transform 
them to numbers from 1 - n). The independent variables consist of 0/1 data 
(species). 
If I do 
tree(locations~factor(species1)+factor(species2)+.....+factor(speciesn), 
sp_data) 
I receive the same results as without the factor() part. 
BTW just a subset of the locations are displayed what is pretty weird 
considering that I included all locations in the analysis.

Martin 


> 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
>
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-- 
Martin Wegmann

DLR - German Aerospace Center
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&&
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University of Wuerzburg
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