Naive Bayes predicting the same label

[alonsopg]

I am figuring out which is the best machine learning approach to use for a pedometer project. So far I have gyro and accelerometer data of walking and no walking. When I train and test a Naive Bayes model in my machine I get nearly 70 of accuracy. However, when I port to java and add it to my android app and start using the implementation it is just predicting the same label. Several question arise from this: why is this happening?... Do I need to use an online learning algorithm for this scenario?, the balance of my classes is wrong?

[nok]

Hello, did you test the accuracy of the transpiled estimator?

porter = Porter(clf, language='java')
accuracy = porter.predict_test(X)
print(accuracy)

[alonsopg]

Thanks for the help nok, I got this:

[nok]

0.0 is the worst case scenario. The question is why did the transpiled estimator return always the same label. Can you post the transpiled output? Did you preprocess the data?

[alonsopg]

The transpiled output?... which is that?. My data is just numbers, the weird thing is that when I train without sklearn porter I get 70% of accuracy when I calculate it with acc_score

[nok]

print(Porter(clf, language='java').export()) prints the transpiled estimator. The method predict_test compares the predictions from the original estimator in Python with the predictions from your target programming language. So the accuracy of your trained estimator doesn't matter.

[alonsopg]

This is the transpiled estimator:

class Brain {

    public static int predict(double[] atts) {
        if (atts.length != 3) {
            return -1;
        }
        int i, j;

        double[] priors = {0.72410256410256413, 0.27589743589743587};
        double[][] sigmas = {{7777.674409056468, 2946.6863403262582, 1470.3790926152326}, {20368.196235029616, 7677.4899510244086, 3792.4066470154612}};
        double[][] thetas = {{2.1022332039660077, -1.1895209475920669, 2.4095972967422088}, {1.1423813271375469, -4.613826715613385, 6.9545192825278832}};
        double[] likelihoods = new double[2];

        for (i = 0; i < 2; i++) {
            double sum = 0.;
            for (j = 0; j < 3; j++) {
                sum += Math.log(2. * Math.PI * sigmas[i][j]);
            }
            double nij = -0.5 * sum;
            sum = 0.;
            for (j = 0; j < 3; j++) {
                sum += Math.pow(atts[j] - thetas[i][j], 2.) / sigmas[i][j];
            }
            nij -= 0.5 * sum;
            likelihoods[i] = Math.log(priors[i]) + nij;
        }

        double highestLikeli = Double.NEGATIVE_INFINITY;
        int classIndex = -1;
        for (i = 0; i < 2; i++) {
            if (likelihoods[i] > highestLikeli) {
                highestLikeli = likelihoods[i];
                classIndex = i;
            }
        }
        return classIndex;
    }

    public static void main(String[] args) {
        if (args.length == 3) {
            double[] atts = new double[args.length];
            for (int i = 0, l = args.length; i < l; i++) {
                atts[i] = Double.parseDouble(args[i]);
            }
            System.out.println(Brain.predict(atts));
        }
    }
}

[nok]

Okay, that looks good. Can you post some samples which you used for the training (.fit())?

[alonsopg]

@nok Here is the data I am using to train the model. I am still having issues in the java side, don't understand why I am always predicting the same label. Here's how I am using the prediction method:

] = rollValue;
    values[1] = pitchValue;
    values[2] = yawValue;
    //values[3] = gxValue;
    //values[4] = gyValue;
    //values[5] = gzValue;

    int y_pred = Brain.predict(values);

    ClassifierLog.setText(Integer.toString(y_pred));

    System.out.println("pred: " + Integer.toString(y_pred));

    int counter = 0;

    //Simple threshold
    if (rollValue < -40 && rollValue > -80
      && pitchValue < 0 && yawValue > 0
      && gxValue < 1000 && gxValue > -2000
      && gyValue < 500 && gyValue > -1000
      && gzValue < 1000 && gzValue > -2000) {
        ClassifierLog.setText("N");                                                 
        System.out.println("COUNTER: " + counter);

    } else {
        counter++;                                         
        ClassifierLog.setText("W");                                               
        System.out.println("COUNTER: " + counter);
    }
}

[nok]

Hello @alonsopg ,

first of all sorry for my late response. Can you share your data again please? And I guess you use the default parameters for the GaussianNB classifier?

Best, Darius