Re: [Java-ML-support] NullPointerException during NaiveBayesClassifier.buildClassifier()

[Thomas A. <th...@ab...>]

Hi Tom,

Did you set class labels in the method buildTrainingDataset?

Training data needs class labels.

You'll need to provide a fully contained working code sample to get more 
help. We can't help you if the two methods that create the objects that 
are responsible for the exception are not provided.

cheers,
Thomas

On 11/11/2012 4:29 PM, Tom Deering wrote:
> I am new to Java-ML, so I apologize if the answer to this is trivial:
>
> I'm trying to construct and use a Classifier in the following way:
>
>         // Construct an instance of the selected classifier
>         Classifier c = constructClassifier(classifier); // This 
> returns a NaiveBayesClassifier
>         ...
>         // Build a training Dataset for the symbol using the 
> historical data
>         Dataset trainingData = buildTrainingDataset(dataArr, 
> sampleIntervalWidth, futureDays);
>         ...
>         // Train the classifier
> c.buildClassifier(trainingData); // NullPointerException happens here
>         ...
>         // Now, classify against the latest sample
>         DenseInstance latestSample = new 
> DenseInstance(buildSampleDoubleArr(dataArr, dataArr.length - 
> sampleIntervalWidth - 1, sampleIntervalWidth));
>         ...
>         // Store the result
>         results.put(s, (Double)c.classify(latestSample));
>
> Each time I try this, I seem to be getting a NullPointerException from 
> the innards of AbstractBayesianClassifier with the following stack trace:
>
> Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
> at 
> net.sf.javaml.classification.bayes.AbstractBayesianClassifier.calculateClassFreqs(AbstractBayesianClassifier.java:207)
> at 
> net.sf.javaml.classification.bayes.AbstractBayesianClassifier.buildClassifier(AbstractBayesianClassifier.java:103)
> at 
> net.sf.javaml.classification.bayes.NaiveBayesClassifier.buildClassifier(NaiveBayesClassifier.java:42)
> at tdeering.iastate.cs572.ainvestor.engine.Engine.rank(Engine.java:106)
>
> Can anyone tell me what I am doing wrong? Am I missing a step where I 
> tell my Classfier about all possible classes?
>
> Thanks,
>
> Tom
>
>
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