Question

I want to classify really long lines of texts. Strings.

Here is the error I am getting:

Exception in thread "main" java.lang.IllegalStateException: No input instance format defined
at weka.filters.unsupervised.attribute.StringToWordVector.input(StringToWordVector.java:681)
at org.berlin.weka.test.TestWeka.main(TestWeka.java:61)

Here is the code but I keep getting exceptions, maybe this is not setup correctly.

package org.berlin.weka.test;

import weka.classifiers.Classifier;
import weka.classifiers.functions.SMO;
import weka.core.Attribute;
import weka.core.FastVector;
import weka.core.Instance;
import weka.core.Instances;
import weka.filters.Filter;
import weka.filters.unsupervised.attribute.StringToWordVector;

public class TestWeka {

    /*
     * java -cp %WEKA_HOME% 
       weka.classifiers.meta.FilteredClassifier 
       -t ReutersAcq-train.arff 
       -T ReutersAcq-test.arff 
       -W "weka.classifiers.functions.SMO -N 2" 
       -F "weka.filters.unsupervised.attribute.StringToWordVector -S"
     */

    public static void main(final String [] args) throws Exception {
        System.out.println("Running");

        final StringToWordVector filter = new StringToWordVector();
        final Classifier classifier = new SMO(); 

        // Create numeric attributes.
        final String[] keywords = { "test1", "test2"};
        FastVector attributes = new FastVector(keywords.length + 1);
        for (int i = 0 ; i < keywords.length; i++) {
          attributes.addElement(new Attribute(keywords[i]));
        }        
        // Add class attribute.
        final FastVector classValues = new FastVector(2);
        classValues.addElement("miss");
        classValues.addElement("hit");

        attributes.addElement(new Attribute("Class", classValues));

        final Instances data = new Instances("Data1", attributes, 100);
        data.setClassIndex(data.numAttributes() - 1);

        ///////////

        Instance instance = new Instance(10);
        instance.setDataset(data);
        // instance.setValue(testset.attribute(0),testset.attribute(0).addStringValue(obj.toString()));
        System.out.println("==>." + data.attribute(0));
        instance.setValue(data.attribute(0), data.attribute(0).addStringValue("test1"));
        instance.setDataset(data);

        // Add class value to instance.
        instance.setClassValue(1.0);

        // Add instance to training data.
        data.add(instance);

        // Use filter.
        filter.input(instance);
        Instances filteredData = Filter.useFilter(data, filter);

        // Rebuild classifier.
        classifier.buildClassifier(filteredData);               
    }

} // End of the class //

Answer 1

Can you try by setting the input format first as following :

//rest of your code

// Use filter
filter.input(instance);
filter.setInputFormat(data); //data instances that you are going to input to the filter
Instances filteredData = Filter.useFilter(data, filter);


For example , you can refer to http://weka.wikispaces.com/Use+WEKA+in+your+Java+code
and Remove filter. (notice that they set input format of the filter before passing instances to filter)