public Number getValue(Comparable row, Comparable column) {
        List l = (List) this.data.getObject(row, column);
        double average = 0.0d;
        int count = 0;
        if (l != null && l.size() > 0) {
            for (int i = 0; i < l.size(); i++) {
                Number n = (Number) l.get(i);
                average += n.doubleValue();
                count += 1;
            }
            if (count > 0) {
                average = average / count;
            }
        }
        if (count == 0) {
            return null;
        }
        return new Double(average);