XYItemRenderer renderer2 = new StandardXYItemRenderer(StandardXYItemRenderer.SHAPES, null);
        plot.setSecondaryDataset(0, series1);
        plot.setSecondaryRenderer(0, renderer2);

        // make the chart...
        JFreeChart chart = new JFreeChart(title, JFreeChart.DEFAULT_TITLE_FONT, plot, true);
        chart.setBackgroundPaint(new GradientPaint(0, 0, Color.white, 0, 1000, Color.blue));

        // and present it in a frame...
        JFrame frame = new ChartFrame(frameTitle, chart);
        frame.pack();
        RefineryUtilities.positionFrameRandomly(frame);
        frame.show();

    }

    /**
     * Displays an horizontally combined XYPlot with X and Y symbolic data.
     *
     * @param frameTitle  the frame title.
     * @param data1  the dataset 1.
     * @param data2  the dataset 2.
     */
    private static void displayXYSymbolicCombinedHorizontally(String frameTitle,
                                                              XYDataset data1, XYDataset data2) {

        String title = "Pollutant Horizontally Combined";
        String x1AxisLabel = "Contamination";
        String x2AxisLabel = "Type";
        String yAxisLabel = "Pollutant";

        // combine the y symbolic values of the two data sets
        String[] combinedYSymbolicValues =
            SampleXYSymbolicDataset.combineYSymbolicDataset((YisSymbolic) data1,
                                                            (YisSymbolic) data2);

        // make master dataset...
        CombinedDataset data = new CombinedDataset();
        data.add(data1);
        data.add(data2);

        // decompose data...
        XYDataset series0 = new SubSeriesDataset(data, 0);
        XYDataset series1 = new SubSeriesDataset(data, 1);

        JFreeChart chart = null;

        // common horizontal and vertical axes
        SymbolicAxis hsymbolicAxis0
            = new SymbolicAxis(x1AxisLabel, ((XisSymbolic) data1).getXSymbolicValues());
        SymbolicAxis hsymbolicAxis1
            = new SymbolicAxis(x2AxisLabel, ((XisSymbolic) data2).getXSymbolicValues());
        SymbolicAxis symbolicAxis
            = new SymbolicAxis(yAxisLabel, combinedYSymbolicValues);

        // create main plot...
        CombinedDomainXYPlot mainPlot = new CombinedDomainXYPlot(symbolicAxis);

        // add subplots...
        XYItemRenderer renderer = new StandardXYItemRenderer(StandardXYItemRenderer.SHAPES, null);
        XYPlot subplot0 = new XYPlot(series0, hsymbolicAxis0, null, renderer);
        XYPlot subplot1 = new XYPlot(series1, hsymbolicAxis1, null, renderer);
        mainPlot.add(subplot0, 1);
        mainPlot.add(subplot1, 1);

        // make the top level JFreeChart object
        chart = new JFreeChart(title, JFreeChart.DEFAULT_TITLE_FONT, mainPlot, true);
        chart.setBackgroundPaint(new GradientPaint(0, 0, Color.white, 0, 1000, Color.blue));

        // and present it in a frame...
        JFrame frame = new ChartFrame(frameTitle, chart);
        frame.pack();
        RefineryUtilities.positionFrameRandomly(frame);
        frame.show();

    }

    /**
     * Vertically combined sample1 and sample2 and display it.
     *
     * @param frameTitle  the frame title.
     * @param data1  the dataset 1.
     * @param data2  the dataset 2.
     */
    private static void displayXYSymbolicCombinedVertically(String frameTitle,
                                                            XYDataset data1, XYDataset data2) {

        String title = "Pollutant Vertically Combined";
        String xAxisLabel = "Contamination and Type";
        String yAxisLabel = "Pollutant";

        // combine the x symbolic values of the two data sets
        String[] combinedXSymbolicValues
            = SampleXYSymbolicDataset.combineXSymbolicDataset((XisSymbolic) data1,
                                                              (XisSymbolic) data2);

        // make master dataset...
        CombinedDataset data = new CombinedDataset();
        data.add(data1);
        data.add(data2);

        // decompose data...
        XYDataset series0 = new SubSeriesDataset(data, 0);
        XYDataset series1 = new SubSeriesDataset(data, 1);

        // common horizontal and vertical axes
        SymbolicAxis hsymbolicAxis
            = new SymbolicAxis(xAxisLabel, combinedXSymbolicValues);

        SymbolicAxis vsymbolicAxis0
            = new SymbolicAxis(yAxisLabel, ((YisSymbolic) data1).getYSymbolicValues());

        SymbolicAxis vsymbolicAxis1
            = new SymbolicAxis(yAxisLabel, ((YisSymbolic) data2).getYSymbolicValues());

        // create the main plot...
        CombinedDomainXYPlot mainPlot = new CombinedDomainXYPlot(hsymbolicAxis);

        // add the sub-plots...
        XYItemRenderer renderer = new StandardXYItemRenderer(StandardXYItemRenderer.SHAPES, null);
        XYPlot subplot0 = new XYPlot(series0, null, vsymbolicAxis0, renderer);
        XYPlot subplot1 = new XYPlot(series1, null, vsymbolicAxis1, renderer);

        mainPlot.add(subplot0, 1);
        mainPlot.add(subplot1, 1);

        // make the chart...
        JFreeChart chart = new JFreeChart(title, JFreeChart.DEFAULT_TITLE_FONT, mainPlot, true);
        chart.setBackgroundPaint(new GradientPaint(0, 0, Color.white, 0, 1000, Color.blue));

        // and present it in a frame...
        JFrame frame = new ChartFrame(frameTitle, chart);
        frame.pack();
        RefineryUtilities.positionFrameRandomly(frame);
        frame.show();

    }

    /**
     * Transform an primitive array to an object array.
     *
     * @param arr  the array.
     *
     * @return an array.
     */
    private static Object toArray(Object arr) {

        if (arr == null) {
            return arr;
        }

        Class cls = arr.getClass();
        if (!cls.isArray()) {
            return arr;
        }

        Class compType = cls.getComponentType();
        int dim = 1;
        while (!compType.isPrimitive()) {
            if (!compType.isArray()) {
                return arr;
            }
            else {
                dim++;
                compType = compType.getComponentType();
            }
        }

        int[] length = new int[dim];
        length[0] = Array.getLength(arr);
        Object[] newarr = null;

        try {
            if (compType.equals(Integer.TYPE)) {
                newarr = (Object[]) Array.newInstance(Class.forName("java.lang.Integer"), length);
            }
            else if (compType.equals(Double.TYPE)) {
                newarr = (Object[]) Array.newInstance(Class.forName("java.lang.Double"), length);
            }
            else if (compType.equals(Long.TYPE)) {
                newarr = (Object[]) Array.newInstance(Class.forName("java.lang.Long"), length);
            }
            else if (compType.equals(Float.TYPE)) {
                newarr = (Object[]) Array.newInstance(Class.forName("java.lang.Float"), length);
            }
            else if (compType.equals(Short.TYPE)) {
                newarr = (Object[]) Array.newInstance(Class.forName("java.lang.Short"), length);
            }
            else if (compType.equals(Byte.TYPE)) {
                newarr = (Object[]) Array.newInstance(Class.forName("java.lang.Byte"), length);
            }
            else if (compType.equals(Character.TYPE)) {
                newarr = (Object[]) Array.newInstance(Class.forName("java.lang.Character"), length);
            }
            else if (compType.equals(Boolean.TYPE)) {
                newarr = (Object[]) Array.newInstance(Class.forName("java.lang.Boolean"), length);
            }
        }
        catch (ClassNotFoundException ex) {
            System.out.println(ex);
        }

        for (int i = 0; i < length[0]; i++) {
            if (dim != 1) {
                newarr[i] = toArray(Array.get(arr, i));
            }
            else {
                newarr[i] = Array.get(arr, i);
            }
        }
        return newarr;
    }

    /**
     * Starting point for the application.
     *
     * @param args  ignored.
     */
    public static void main(String[] args) {

        SampleXYSymbolicDataset s1 = createXYSymbolicSample1();
        SampleXYSymbolicDataset s2 = createXYSymbolicSample2();

        displayXYSymbolic("Example 1", s1, "Pollutant", "contamination", "pollutant");

        displayXYSymbolic("Example 2", s2, "Pollutant", "type", "pollutant");

        displayXYSymbolicCombinedHorizontally("Example 3", (SampleXYSymbolicDataset) s1.clone(),
                                                           (SampleXYSymbolicDataset) s2.clone());

        displayXYSymbolicCombinedVertically("Example 4", (SampleXYSymbolicDataset) s1.clone(),
                                                         (SampleXYSymbolicDataset) s2.clone());

        displayXYSymbolicOverlaid("Example 5", (SampleXYSymbolicDataset) s1.clone(),
                                               (SampleXYSymbolicDataset) s2.clone());

    }

}