public class FirstJobReducer extends Reducer<Text, Text, Text, Text> {

    private ArrayList<Text> cache;

    @Override
    public void reduce(Text carCategory, Iterable<Text> distance, Context context) throws IOException, InterruptedException {

        this.cache = new ArrayList<>();
        double count = 0;
        long totalDistance = 0;

        for (Text d : distance) {
            totalDistance += (long)Double.parseDouble(d.toString());
            cache.add(d);
            count++;
        }

        double average = totalDistance / count;
        double variance = 0;

        for (Text d : cache) {
            variance += Math.pow((Double.parseDouble(d.toString()) - average), 2);
        }

        variance = variance / count;
        String result = String.format("%.2f", average) + ";" + String.format("%.2f", variance) + ";" + totalDistance;

        context.write(carCategory, new Text(result));
    }
}