Reporting Trend Line

Question

How would you create a line in JasperReports that follows the trend for the data, in addition to showing the data points? Here are before and after shots:

Before

After

The Time Series report does not appear to have any such option to draw the orange line. (The orange line should be smooth, and thinner, but that's the general idea.)

Any ideas how to craft such a report with iReport 3.7.1?

Answer 1

One solution requires the following items:

• BezierLineCustomizer to make the lines curved.
• RunningAverageIncrementer to calculate a running average based on a variable.
• iReport variable that uses the RunningAverageIncremeter.

BezierLineCustomizer Class

public class BezierLineCustomizer
  implements JRChartCustomizer {
  public BezierLineCustomizer() {
  }

  public void customize( JFreeChart jFreeChart, JRChart jrChart ) {
    XYPlot xyPlot = ( XYPlot )jFreeChart.getPlot();

    XYSplineRenderer splineRenderer = new XYSplineRenderer();

    // Make the spline line thick and orange.
    //
    splineRenderer.setSeriesShapesVisible( 0, false );
    splineRenderer.setSeriesShapesVisible( 1, false );
    splineRenderer.setSeriesLinesVisible( 1, false );
    splineRenderer.setSeriesStroke(
        0, new BasicStroke(
            4.0f, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND,
            1.0f, null, 0.0f
        )
    );

    splineRenderer.setSeriesPaint( 0, new Color( 255, 140, 0 ) );
    splineRenderer.setSeriesVisibleInLegend( 1, Boolean.FALSE );

    // Duplicate the data into a new dataset to control its line independently.
    //
    xyPlot.setDataset( 1, xyPlot.getDataset(0) );

    XYItemRenderer defaultRenderer = new XYLineAndShapeRenderer();
    defaultRenderer.setSeriesVisible( 0, Boolean.FALSE );
    defaultRenderer.setSeriesVisibleInLegend( 0, Boolean.FALSE );

    xyPlot.setRenderer( 1, defaultRenderer );
    xyPlot.setRenderer( 0, splineRenderer );
  }
}

RunningAverageIncrementer Class

public class RunningAverageIncrementer
  implements JRIncrementer {
  /** Default number of tallies. */
  private static final int DEFAULT_TALLIES = 128;

  /** Number of tallies within the sliding window. */
  private static final int DEFAULT_SLIDING_WINDOW_SIZE = 30;

  /** Stores a sliding window of values. */
  private List<Double> values = new ArrayList<Double>( DEFAULT_TALLIES );

  /**
   * Instantiated by the RunningAverageIncrementerFactory class.
   */
  public RunningAverageIncrementer() {
  }

  /**
   * Calculates the average of previously known values.
   * @return The average of the list of values returned by getValues().
   */
  private double calculateAverage() {
    double result = 0.0;
    List<Double> values = getValues();

    for( Double d: getValues() ) {
      result += d.doubleValue();
    }

    return result / values.size();
  }

  /**
   * Called each time a new value to be averaged is received.
   * @param value The new value to include for the average.
   */
  private void recordValue( Double value ) {
    List<Double> values = getValues();

    // Throw out 
    //
    if( values.size() > getSlidingWindowSize() ) {
      values.remove( 0 );
    }

    this.values.add( value );
  }

  private List<Double> getValues() {
    return values;
  }

  private int getIterations() {
    return getValues().size();
  }

  /**
   * Returns the newly incremented value, which is calculated by averaging
   * the previous value from the previous call to this method.
   * 
   * @param jrFillVariable Unused.
   * @param tally New data point to average.
   * @param abstractValueProvider Unused.
   * @return The newly incremented value.
   */
  public Object increment( JRFillVariable jrFillVariable, Object tally, 
                           AbstractValueProvider abstractValueProvider ) {
    double value = ((Number)tally).doubleValue();

    recordValue( value );

    double previousAverage = calculateAverage();
    double newAverage = 
      ( ( value - previousAverage ) / ( getIterations() + 1 ) ) + previousAverage;

    return new BigDecimal( newAverage );
  }

  protected int getSlidingWindowSize() {
    return DEFAULT_SLIDING_WINDOW_SIZE;
  }
}

iReport Variable

Create a variable that uses the RunningAverageIncrementerFactory class (exercise left to the reader). Set its variable expression to the plotted value. Set its initial value expression to zero.

Spline

Set the Customizer Class property of the TimeSeries chart to use the BezierLineCustomizer class.

Result

After these modifications, the running average is clearly visible: