machinelearning.KnnClassifier.java Source code

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Here is the source code for machinelearning.KnnClassifier.java

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package machinelearning;

import java.util.Map;
import java.util.TreeMap;
import weka.classifiers.Classifier;
import weka.core.Instance;
import weka.core.Instances;

/**
 *
 * @author Schuyler
 */
public class KnnClassifier extends Classifier {
    private Instances trainingData;

    @Override
    public void buildClassifier(Instances data) throws Exception {
        trainingData = data;
    }

    @Override
    public double classifyInstance(Instance instance) {
        return this.classifyInstance(instance, 3);
    }

    public double classifyInstance(Instance instance, int k) {
        int size = trainingData.numInstances();
        int attributes = trainingData.numAttributes() - 1;
        float dist;
        Map<Float, Instance> neighbors = new TreeMap<>();

        Instance test;

        for (int i = 0; i < size; i++) {
            dist = 0;
            test = trainingData.instance(i);

            for (int j = 0; j < attributes; j++) {
                if (test.attribute(j).isNominal()) {
                    if (instance.attribute(j).equals(test.attribute(j)))
                        dist++;
                } else
                    dist += Math.abs(test.value(test.attribute(j)) - instance.value(test.attribute(j)));
            }

            neighbors.put(dist, test);
        }

        return findMostCommon(neighbors, k);
    }

    private double findMostCommon(Map<Float, Instance> neighbors, int k) {
        int count = 0;
        int[] classCount = new int[trainingData.numClasses()];
        double classGuess = -1;
        int classSize = 0;
        int index = trainingData.firstInstance().classIndex();

        for (Map.Entry<Float, Instance> entry : neighbors.entrySet()) {
            if (count == k)
                break;

            classCount[(int) entry.getValue().value(index)]++;

            if (classCount[(int) entry.getValue().value(index)] > classSize) {
                classGuess = entry.getValue().value(index);
                classSize = classCount[(int) entry.getValue().value(index)];
            }

            count++;
        }

        return classGuess;
    }
}