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List:       wekalist
Subject:    R: [Wekalist] Build your own Instances: error
From:       "Cosimo Palmisano" <c.palmisano () poliba ! it>
Date:       2006-02-24 18:00:53
Message-ID: 200602241750.k1OHo5Zv011413 () mail ! poliba ! it
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In your opinion what are the hierarchical clustering algorithms. I
identified the cobweb. Are there any others implemented in weka?

Ciao 

-----Messaggio originale-----
Da: Daniel Midgley [mailto:dmidgley@cyllene.uwa.edu.au] 
Inviato: venerd́ 24 febbraio 2006 6.08
A: wekalist@list.scms.waikato.ac.nz
Oggetto: [Wekalist] Build your own Instances: error

Hello.

I'm trying to get into Weka's classes to hork some info out of certain
methods.
But I'm getting an error.

Here's what I'm doing:
1) I successfully create a new FileReader (from java.io.FileReader (string),
and the string I give it is the name of an .arff file.  
(e.g. "Weather.arff")
2) I successfully create an Instances(Reader) object (from
weka.core.Instances), passing the FileReader to Instances as an argument.
3) I successfully create a Classifier ( let's just pick
weka.classifiers.trees.J48() )

4) Now here comes the problem. I try to call my new Classifier's
buildClassifier method. I pass it the name of my new Instances object, and
it throws an exception.

weka.core.Instances:355
UnassignedClassException
Class index is negative(not set)! in weka.core.Instances

Clearly I'm running afoul of the classAttribute() method in Instances, but I
can't figure out how to get past it, or what I'm doing wrong.

My ultimate goal is to use the DistributionForInstances method on a
Classifier object.

Any ideas?

Thanks,
Daniel
=-=-=-=-=-=-=-=-=-=-=-=-=
Daniel Midgley
University of Western Australia, Linguistics dmidgley at cyllene dot uwa dot
edu dot au =-=-=-=-=-=-=-=-=-=-=-=-=







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