Shannon Entropy Calculation

    public static double entropy(List<? extends Comparable> values) {

        final Map<Comparable, Long> valueOccurances = new HashMap<Comparable, Long>();

        for (Comparable value : values) {
            Long valueOccurance = valueOccurances.get(value);
            valueOccurances.put(value, valueOccurance == null ? 1L : ++valueOccurance);
        }

        double combinedEntropy = 0.0d;

        for (Comparable value : valueOccurances.keySet()) {
            double entropy = valueOccurances.get(value) / (double) values.size();
            combinedEntropy += entropy * (Math.log(entropy) / Math.log(2));
        }

        return -combinedEntropy;
    }