double minimum = 0.0;
            int categoryCount = dataset.getRowCount();
            for (int item = 0; item < categoryCount; item++) {
                double total = 0.0;

                int seriesCount = dataset.getColumnCount();
                for (int series = 0; series < seriesCount; series++) {
                    Number number = dataset.getValue(series, item);
                    if (number != null) {
                        double value = number.doubleValue();
                        if (value < 0.0) {
                            total = total + value;
                            // '+', remember value is negative
                        }
                    }
                }
                minimum = Math.min(minimum, total);

            }
            result = new Double(minimum);