Average Resultant acceleration

gistfile1.java

/**
 * @return Double resultant = 1/n * ∑ √(x² + y² + z²)
 */
public static double computeResultantAcc(JavaRDD<double[]> data) {
  // first let's compute the square of each value and the sum
  // compute then the root square: √(x² + y² + z²)
  // to finish apply a mean function: 1/n * sum [√(x² + y² + z²)]
  JavaRDD<Vector> squared = data.map(record -> Math.pow(record[0], 2)
                                             + Math.pow(record[1], 2)
                                             + Math.pow(record[2], 2))
                                .map(Math::sqrt)
                                .map(sum -> Vectors.dense(new double[]{sum}));

  return Statistics.colStats(squared.rdd()).mean().toArray()[0];

}