org.eclipse.modisco.utils.chart.birt.core/src/org/eclipse/modisco/utils/chart/birt/core/internal/exported/BirtGraphHelper.java - modisco/org.eclipse.modisco - Git at Google

 /*******************************************************************************
  * Copyright (c) 2012 INRIA. All rights reserved. This program and the
  * accompanying materials are made available under the terms of the Eclipse
  * Public License v1.0 which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors: Guillaume Doux - INRIA - Initial API and implementation
  *
  ******************************************************************************/
 package org.eclipse.modisco.utils.chart.birt.core.internal.exported;

 import java.io.File;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Comparator;
 import java.util.List;

 import org.eclipse.birt.chart.computation.Point;
 import org.eclipse.birt.chart.device.IDeviceRenderer;
 import org.eclipse.birt.chart.exception.ChartException;
 import org.eclipse.birt.chart.factory.GeneratedChartState;
 import org.eclipse.birt.chart.factory.Generator;
 import org.eclipse.birt.chart.model.ChartWithAxes;
 import org.eclipse.birt.chart.model.attribute.Anchor;
 import org.eclipse.birt.chart.model.attribute.AxisType;
 import org.eclipse.birt.chart.model.attribute.Bounds;
 import org.eclipse.birt.chart.model.attribute.ChartDimension;
 import org.eclipse.birt.chart.model.attribute.ColorDefinition;
 import org.eclipse.birt.chart.model.attribute.LegendItemType;
 import org.eclipse.birt.chart.model.attribute.LineAttributes;
 import org.eclipse.birt.chart.model.attribute.LineStyle;
 import org.eclipse.birt.chart.model.attribute.impl.BoundsImpl;
 import org.eclipse.birt.chart.model.attribute.impl.ColorDefinitionImpl;
 import org.eclipse.birt.chart.model.attribute.impl.LineAttributesImpl;
 import org.eclipse.birt.chart.model.attribute.impl.NumberFormatSpecifierImpl;
 import org.eclipse.birt.chart.model.component.Axis;
 import org.eclipse.birt.chart.model.component.Series;
 import org.eclipse.birt.chart.model.component.impl.SeriesImpl;
 import org.eclipse.birt.chart.model.data.NumberDataSet;
 import org.eclipse.birt.chart.model.data.SeriesDefinition;
 import org.eclipse.birt.chart.model.data.impl.NumberDataSetImpl;
 import org.eclipse.birt.chart.model.data.impl.SeriesDefinitionImpl;
 import org.eclipse.birt.chart.model.impl.ChartWithAxesImpl;
 import org.eclipse.birt.chart.model.type.LineSeries;
 import org.eclipse.birt.chart.model.type.impl.LineSeriesImpl;
 import org.eclipse.birt.chart.util.PluginSettings;
 import org.eclipse.modisco.utils.chart.birt.core.internal.GraphHelperException;
 import org.eclipse.modisco.utils.chart.metamodel.internal.chart.Axe;
 import org.eclipse.modisco.utils.chart.metamodel.internal.chart.Chart;
 import org.eclipse.modisco.utils.chart.metamodel.internal.chart.Coordinate;
 import org.eclipse.modisco.utils.chart.metamodel.internal.chart.Serie;

 /**
  * Class providing support for generating a chart with Birt in png
  * The chart is generated from a birtchart model @see org.eclipse.modisco.utils.chart.metamodel
  * @author Guillaume Doux
  *
  */

 public final class BirtGraphHelper {

 	private static final double UNIT_SPACING = 0.1;

 	private static BirtGraphHelper instance;

 	private List<ColorDefinition> colors;

 	private static final int CHART_WIDTH = 800;

 	private static final int CHART_HEIGHT = 400;

 	public List<ColorDefinition> getColors() {
 		return this.colors;
 	}

 	public void setColors(final List<ColorDefinition> colors) {
 		this.colors = colors;
 	}

 	private BirtGraphHelper() {
 		this.colors = new ArrayList<ColorDefinition>();
 		this.colors.add(ColorDefinitionImpl.BLUE());
 		this.colors.add(ColorDefinitionImpl.ORANGE());
 		this.colors.add(ColorDefinitionImpl.GREEN());
 		this.colors.add(ColorDefinitionImpl.RED());
 		this.colors.add(ColorDefinitionImpl.CYAN());
 		this.colors.add(ColorDefinitionImpl.PINK());
 		this.colors.add(ColorDefinitionImpl.GREY());
 		this.colors.add(ColorDefinitionImpl.YELLOW());
 	}

 	/**
 	 * Give an instance of the chart generator
 	 * @return the BirtGraphHelper
 	 */
 	public static synchronized BirtGraphHelper getInstance() {
 		if (BirtGraphHelper.instance == null) {
 			BirtGraphHelper.instance = new BirtGraphHelper();
 		}
 		return BirtGraphHelper.instance;
 	}

 	/**
 	 * Create a Birt chart using the chart passed with the birtchart parameter
 	 * Works only with graph having 2 dimensions
 	 * @param birtChart
 	 * @param targetFolder
 	 * @param fileName+".png" name of the png file (without extension)
 	 * @throws ChartException, Exception
 	 */
 	public void createBirtGraph(final Chart birtChart,
 			final File targetFolder, final String fileName) throws Exception {
 		ChartWithAxes chart = ChartWithAxesImpl.create();
 		if (birtChart.getAxes().size() == 2) {
 			chart.setDimension(ChartDimension.TWO_DIMENSIONAL_LITERAL);
 		} else {
 			throw new GraphHelperException("the chart should have only 2 dimensions");
 		}
 		chart.setUnitSpacing(BirtGraphHelper.UNIT_SPACING);
 		chart.getPlot().setBackground(ColorDefinitionImpl.WHITE());
 		chart.getPlot().getClientArea().setBackground(ColorDefinitionImpl.WHITE());
 		chart.getLegend().setItemType(LegendItemType.SERIES_LITERAL);
 		chart.getLegend().setVisible(true);
 		chart.getLegend().setAnchor(Anchor.NORTH_EAST_LITERAL);

 		chart.getTitle().getLabel().getCaption()
 		.setValue(birtChart.getTitle());

 		final Axe abs = birtChart.getAxes().get(0);
 		final Axe ord = birtChart.getAxes().get(1);

 		final Axis xAxis = chart.getPrimaryBaseAxes()[0];
 		xAxis.setType(AxisType.LINEAR_LITERAL);
 		xAxis.setFormatSpecifier(NumberFormatSpecifierImpl.create());

 		xAxis.getTitle().getCaption().setValue(abs.getLegend() + " (" + abs.getUnit() + ")"); //$NON-NLS-1$
 		xAxis.getTitle().setVisible(true);

 		final List<Point> dataPoints = new ArrayList<Point>();

 		final SeriesDefinition ySeriesDefinition = SeriesDefinitionImpl.create();

 		final Comparator<Point> comparator = new Comparator<Point>() {
 			public int compare(final Point point1, final Point point2) {
 				if (point1.x == point2.x) {
 					return 0;
 				} else if (point1.x < point2.x) {
 					return -1;
 				} else {
 					return 1;
 				}
 			}
 		};
 		for (Serie serie : birtChart.getSeries()) {
 			dataPoints.clear();
 			for (org.eclipse.modisco.utils.chart.metamodel.internal.chart.Point point : serie.getPoints()) {
 				double xCoord = 0;
 				double yCoord = 0;
 				for (Coordinate coord : point.getCoordinates()) {
 					if (coord.getAxe().equals(abs)) {
 						xCoord = coord.getValue();
 					}
 					if (coord.getAxe().equals(ord)) {
 						yCoord = coord.getValue();
 					}
 				}
 				final Point birtPoint = new Point(xCoord, yCoord);
 				dataPoints.add(birtPoint);
 			}

 			// sort on X axis

 			Collections.sort(dataPoints, comparator);


 			final ColorDefinition serieColor = getColorForSerie(birtChart.getSeries().indexOf(serie));


 			final LineSeries lineSeries = (LineSeries) LineSeriesImpl.create();
 			lineSeries.setSeriesIdentifier(serie.getName());
 			lineSeries.setCurve(false);

 			final ArrayList<Double> yAxisValues = new ArrayList<Double>();
 			for (Point dataPoint : dataPoints) {
 				yAxisValues.add(dataPoint.y);
 			}
 			final NumberDataSet dataSet = NumberDataSetImpl.create(yAxisValues);
 			lineSeries.setDataSet(dataSet);
 			lineSeries.getMarkers().clear();//Remove this to show markers for each points

 			final LineAttributes lineAttr = LineAttributesImpl.create(ColorDefinitionImpl.BLACK(),
 					LineStyle.SOLID_LITERAL, 1);
 			lineAttr.setVisible(true);
 			lineAttr.setColor(serieColor);
 			lineSeries.setLineAttributes(lineAttr);

 			final Point[] linearRegression = computeLinearRegression(dataPoints);
 			final LineSeries linearRegSeries = (LineSeries) LineSeriesImpl.create();
 			final ArrayList<Double> regressionYAxisValues = new ArrayList<Double>();
 			for (Point point : linearRegression) {
 					regressionYAxisValues.add(point.y);
 			}
 			final NumberDataSet linearRegDataSet = NumberDataSetImpl.create(regressionYAxisValues);
 			linearRegSeries.setDataSet(linearRegDataSet);
 			linearRegSeries.getMarkers().clear();

 			// line attributes
 			final LineAttributes lineAttr2 = LineAttributesImpl.create(ColorDefinitionImpl.BLACK(),
 					LineStyle.DASHED_LITERAL, 1);
 			lineAttr2.setVisible(true);
 			lineAttr2.setColor(serieColor);
 			linearRegSeries.setLineAttributes(lineAttr2);

 			ySeriesDefinition.getSeries().add(lineSeries);
 			ySeriesDefinition.getSeries().add(linearRegSeries);

 		}

 		final ArrayList<Double> xAxisValues = new ArrayList<Double>();
 		for (Point dataPoint : dataPoints) {
 				xAxisValues.add(dataPoint.x);
 		}
 		final NumberDataSet xAxisDataSet = NumberDataSetImpl.create(xAxisValues);

 		final Series xAxisSeries = SeriesImpl.create();
 		xAxisSeries.setDataSet(xAxisDataSet);
 		final SeriesDefinition xSeriesDefinition = SeriesDefinitionImpl.create();
 		xSeriesDefinition.getSeries().add(xAxisSeries);
 		xAxis.getSeriesDefinitions().add(xSeriesDefinition);

 		final Axis yAxis = chart.getPrimaryOrthogonalAxis(xAxis);
 		yAxis.setType(AxisType.LINEAR_LITERAL);
 		yAxis.setFormatSpecifier(NumberFormatSpecifierImpl.create());
 		yAxis.getTitle().setVisible(true);

 		yAxis.getTitle().getCaption().setValue(ord.getLegend() + " (" + ord.getUnit() + ")"); //$NON-NLS-1$
 		yAxis.getSeriesDefinitions().add(ySeriesDefinition);

 		//Chart rendering
 		final PluginSettings pSettings = PluginSettings.instance();
 		final IDeviceRenderer render = pSettings.getDevice("dv.PNG"); //$NON-NLS-1$
 		render.setProperty(IDeviceRenderer.FILE_IDENTIFIER, new File(targetFolder,
 				fileName + ".png")); //$NON-NLS-1$
 		final Bounds bounds = BoundsImpl.create(0, 0, CHART_WIDTH, CHART_HEIGHT);
 		final Generator generator = Generator.instance();
 		final GeneratedChartState state = generator.build(render.getDisplayServer(), chart, bounds, null,
 				null, null);
 		generator.render(render, state);
 	}


 	private ColorDefinition getColorForSerie(final int indexOf) {
 		return this.colors.get(indexOf % this.colors.size());
 	}


 	/**
 	 * Computes the linear regression of the given list of points, and returns
 	 * points on the computed line.
 	 *
 	 * @param dataPoints
 	 *            the points to include in the computation
 	 * @return points on the computed approximation line, with the same abscissa
 	 *         as the input points
 	 */
 	private static Point[] computeLinearRegression(final List<Point> dataPoints) {
 		// see: http://en.wikipedia.org/wiki/Simple_linear_regression
 		final double size = dataPoints.size();
 		if ((int) size == 0) {
 			return new Point[0];
 		}
 		if ((int) size == 1) {
 			Point point = dataPoints.get(0);
 			return new Point[] { new Point(point.x, point.y) };
 		}
 		double sumXY = 0.0;
 		double sumX = 0.0;
 		double sumY = 0.0;
 		double sumXX = 0.0;
 		for (Point point : dataPoints) {
 			sumX += point.x;
 			sumXX += point.x * point.x;
 			sumY += point.y;
 			sumXY += point.x * point.y;
 		}

 		// a = (NΣXY - (ΣX)(ΣY)) / (NΣX² - (ΣX)²)
 		final double a = (size * sumXY - sumX * sumY) / (size * sumXX - sumX * sumX);
 		// b = (ΣY - b(ΣX)) / N
 		final double b = (sumY - a * sumX) / size;

 		List<Point> resultPoints = new ArrayList<Point>();
 		for (Point point : dataPoints) {
 			// y = ax + b
 			resultPoints.add(new Point(point.x, a * point.x + b));
 		}
 		return resultPoints.toArray(new Point[resultPoints.size()]);
 	}
 }
	/*******************************************************************************
	* Copyright (c) 2012 INRIA. All rights reserved. This program and the
	* accompanying materials are made available under the terms of the Eclipse
	* Public License v1.0 which accompanies this distribution, and is available at
	* http://www.eclipse.org/legal/epl-v10.html
	*
	* Contributors: Guillaume Doux - INRIA - Initial API and implementation
	*
	******************************************************************************/
	package org.eclipse.modisco.utils.chart.birt.core.internal.exported;

	import java.io.File;
	import java.util.ArrayList;
	import java.util.Collections;
	import java.util.Comparator;
	import java.util.List;

	import org.eclipse.birt.chart.computation.Point;
	import org.eclipse.birt.chart.device.IDeviceRenderer;
	import org.eclipse.birt.chart.exception.ChartException;
	import org.eclipse.birt.chart.factory.GeneratedChartState;
	import org.eclipse.birt.chart.factory.Generator;
	import org.eclipse.birt.chart.model.ChartWithAxes;
	import org.eclipse.birt.chart.model.attribute.Anchor;
	import org.eclipse.birt.chart.model.attribute.AxisType;
	import org.eclipse.birt.chart.model.attribute.Bounds;
	import org.eclipse.birt.chart.model.attribute.ChartDimension;
	import org.eclipse.birt.chart.model.attribute.ColorDefinition;
	import org.eclipse.birt.chart.model.attribute.LegendItemType;
	import org.eclipse.birt.chart.model.attribute.LineAttributes;
	import org.eclipse.birt.chart.model.attribute.LineStyle;
	import org.eclipse.birt.chart.model.attribute.impl.BoundsImpl;
	import org.eclipse.birt.chart.model.attribute.impl.ColorDefinitionImpl;
	import org.eclipse.birt.chart.model.attribute.impl.LineAttributesImpl;
	import org.eclipse.birt.chart.model.attribute.impl.NumberFormatSpecifierImpl;
	import org.eclipse.birt.chart.model.component.Axis;
	import org.eclipse.birt.chart.model.component.Series;
	import org.eclipse.birt.chart.model.component.impl.SeriesImpl;
	import org.eclipse.birt.chart.model.data.NumberDataSet;
	import org.eclipse.birt.chart.model.data.SeriesDefinition;
	import org.eclipse.birt.chart.model.data.impl.NumberDataSetImpl;
	import org.eclipse.birt.chart.model.data.impl.SeriesDefinitionImpl;
	import org.eclipse.birt.chart.model.impl.ChartWithAxesImpl;
	import org.eclipse.birt.chart.model.type.LineSeries;
	import org.eclipse.birt.chart.model.type.impl.LineSeriesImpl;
	import org.eclipse.birt.chart.util.PluginSettings;
	import org.eclipse.modisco.utils.chart.birt.core.internal.GraphHelperException;
	import org.eclipse.modisco.utils.chart.metamodel.internal.chart.Axe;
	import org.eclipse.modisco.utils.chart.metamodel.internal.chart.Chart;
	import org.eclipse.modisco.utils.chart.metamodel.internal.chart.Coordinate;
	import org.eclipse.modisco.utils.chart.metamodel.internal.chart.Serie;

	/**
	* Class providing support for generating a chart with Birt in png
	* The chart is generated from a birtchart model @see org.eclipse.modisco.utils.chart.metamodel
	* @author Guillaume Doux
	*
	*/

	public final class BirtGraphHelper {

	private static final double UNIT_SPACING = 0.1;

	private static BirtGraphHelper instance;

	private List<ColorDefinition> colors;

	private static final int CHART_WIDTH = 800;

	private static final int CHART_HEIGHT = 400;

	public List<ColorDefinition> getColors() {
	return this.colors;
	}

	public void setColors(final List<ColorDefinition> colors) {
	this.colors = colors;
	}

	private BirtGraphHelper() {
	this.colors = new ArrayList<ColorDefinition>();
	this.colors.add(ColorDefinitionImpl.BLUE());
	this.colors.add(ColorDefinitionImpl.ORANGE());
	this.colors.add(ColorDefinitionImpl.GREEN());
	this.colors.add(ColorDefinitionImpl.RED());
	this.colors.add(ColorDefinitionImpl.CYAN());
	this.colors.add(ColorDefinitionImpl.PINK());
	this.colors.add(ColorDefinitionImpl.GREY());
	this.colors.add(ColorDefinitionImpl.YELLOW());
	}

	/**
	* Give an instance of the chart generator
	* @return the BirtGraphHelper
	*/
	public static synchronized BirtGraphHelper getInstance() {
	if (BirtGraphHelper.instance == null) {
	BirtGraphHelper.instance = new BirtGraphHelper();
	}
	return BirtGraphHelper.instance;
	}

	/**
	* Create a Birt chart using the chart passed with the birtchart parameter
	* Works only with graph having 2 dimensions
	* @param birtChart
	* @param targetFolder
	* @param fileName+".png" name of the png file (without extension)
	* @throws ChartException, Exception
	*/
	public void createBirtGraph(final Chart birtChart,
	final File targetFolder, final String fileName) throws Exception {
	ChartWithAxes chart = ChartWithAxesImpl.create();
	if (birtChart.getAxes().size() == 2) {
	chart.setDimension(ChartDimension.TWO_DIMENSIONAL_LITERAL);
	} else {
	throw new GraphHelperException("the chart should have only 2 dimensions");
	}
	chart.setUnitSpacing(BirtGraphHelper.UNIT_SPACING);
	chart.getPlot().setBackground(ColorDefinitionImpl.WHITE());
	chart.getPlot().getClientArea().setBackground(ColorDefinitionImpl.WHITE());
	chart.getLegend().setItemType(LegendItemType.SERIES_LITERAL);
	chart.getLegend().setVisible(true);
	chart.getLegend().setAnchor(Anchor.NORTH_EAST_LITERAL);

	chart.getTitle().getLabel().getCaption()
	.setValue(birtChart.getTitle());

	final Axe abs = birtChart.getAxes().get(0);
	final Axe ord = birtChart.getAxes().get(1);

	final Axis xAxis = chart.getPrimaryBaseAxes()[0];
	xAxis.setType(AxisType.LINEAR_LITERAL);
	xAxis.setFormatSpecifier(NumberFormatSpecifierImpl.create());

	xAxis.getTitle().getCaption().setValue(abs.getLegend() + " (" + abs.getUnit() + ")"); //$NON-NLS-1$
	xAxis.getTitle().setVisible(true);

	final List<Point> dataPoints = new ArrayList<Point>();

	final SeriesDefinition ySeriesDefinition = SeriesDefinitionImpl.create();

	final Comparator<Point> comparator = new Comparator<Point>() {
	public int compare(final Point point1, final Point point2) {
	if (point1.x == point2.x) {
	return 0;
	} else if (point1.x < point2.x) {
	return -1;
	} else {
	return 1;
	}
	}
	};
	for (Serie serie : birtChart.getSeries()) {
	dataPoints.clear();
	for (org.eclipse.modisco.utils.chart.metamodel.internal.chart.Point point : serie.getPoints()) {
	double xCoord = 0;
	double yCoord = 0;
	for (Coordinate coord : point.getCoordinates()) {
	if (coord.getAxe().equals(abs)) {
	xCoord = coord.getValue();
	}
	if (coord.getAxe().equals(ord)) {
	yCoord = coord.getValue();
	}
	}
	final Point birtPoint = new Point(xCoord, yCoord);
	dataPoints.add(birtPoint);
	}

	// sort on X axis

	Collections.sort(dataPoints, comparator);


	final ColorDefinition serieColor = getColorForSerie(birtChart.getSeries().indexOf(serie));


	final LineSeries lineSeries = (LineSeries) LineSeriesImpl.create();
	lineSeries.setSeriesIdentifier(serie.getName());
	lineSeries.setCurve(false);

	final ArrayList<Double> yAxisValues = new ArrayList<Double>();
	for (Point dataPoint : dataPoints) {
	yAxisValues.add(dataPoint.y);
	}
	final NumberDataSet dataSet = NumberDataSetImpl.create(yAxisValues);
	lineSeries.setDataSet(dataSet);
	lineSeries.getMarkers().clear();//Remove this to show markers for each points

	final LineAttributes lineAttr = LineAttributesImpl.create(ColorDefinitionImpl.BLACK(),
	LineStyle.SOLID_LITERAL, 1);
	lineAttr.setVisible(true);
	lineAttr.setColor(serieColor);
	lineSeries.setLineAttributes(lineAttr);

	final Point[] linearRegression = computeLinearRegression(dataPoints);
	final LineSeries linearRegSeries = (LineSeries) LineSeriesImpl.create();
	final ArrayList<Double> regressionYAxisValues = new ArrayList<Double>();
	for (Point point : linearRegression) {
	regressionYAxisValues.add(point.y);
	}
	final NumberDataSet linearRegDataSet = NumberDataSetImpl.create(regressionYAxisValues);
	linearRegSeries.setDataSet(linearRegDataSet);
	linearRegSeries.getMarkers().clear();

	// line attributes
	final LineAttributes lineAttr2 = LineAttributesImpl.create(ColorDefinitionImpl.BLACK(),
	LineStyle.DASHED_LITERAL, 1);
	lineAttr2.setVisible(true);
	lineAttr2.setColor(serieColor);
	linearRegSeries.setLineAttributes(lineAttr2);

	ySeriesDefinition.getSeries().add(lineSeries);
	ySeriesDefinition.getSeries().add(linearRegSeries);

	}

	final ArrayList<Double> xAxisValues = new ArrayList<Double>();
	for (Point dataPoint : dataPoints) {
	xAxisValues.add(dataPoint.x);
	}
	final NumberDataSet xAxisDataSet = NumberDataSetImpl.create(xAxisValues);

	final Series xAxisSeries = SeriesImpl.create();
	xAxisSeries.setDataSet(xAxisDataSet);
	final SeriesDefinition xSeriesDefinition = SeriesDefinitionImpl.create();
	xSeriesDefinition.getSeries().add(xAxisSeries);
	xAxis.getSeriesDefinitions().add(xSeriesDefinition);

	final Axis yAxis = chart.getPrimaryOrthogonalAxis(xAxis);
	yAxis.setType(AxisType.LINEAR_LITERAL);
	yAxis.setFormatSpecifier(NumberFormatSpecifierImpl.create());
	yAxis.getTitle().setVisible(true);

	yAxis.getTitle().getCaption().setValue(ord.getLegend() + " (" + ord.getUnit() + ")"); //$NON-NLS-1$
	yAxis.getSeriesDefinitions().add(ySeriesDefinition);

	//Chart rendering
	final PluginSettings pSettings = PluginSettings.instance();
	final IDeviceRenderer render = pSettings.getDevice("dv.PNG"); //$NON-NLS-1$
	render.setProperty(IDeviceRenderer.FILE_IDENTIFIER, new File(targetFolder,
	fileName + ".png")); //$NON-NLS-1$
	final Bounds bounds = BoundsImpl.create(0, 0, CHART_WIDTH, CHART_HEIGHT);
	final Generator generator = Generator.instance();
	final GeneratedChartState state = generator.build(render.getDisplayServer(), chart, bounds, null,
	null, null);
	generator.render(render, state);
	}


	private ColorDefinition getColorForSerie(final int indexOf) {
	return this.colors.get(indexOf % this.colors.size());
	}



	/**
	* Computes the linear regression of the given list of points, and returns
	* points on the computed line.
	*
	* @param dataPoints
	* the points to include in the computation
	* @return points on the computed approximation line, with the same abscissa
	* as the input points
	*/
	private static Point[] computeLinearRegression(final List<Point> dataPoints) {
	// see: http://en.wikipedia.org/wiki/Simple_linear_regression
	final double size = dataPoints.size();
	if ((int) size == 0) {
	return new Point[0];
	}
	if ((int) size == 1) {
	Point point = dataPoints.get(0);
	return new Point[] { new Point(point.x, point.y) };
	}
	double sumXY = 0.0;
	double sumX = 0.0;
	double sumY = 0.0;
	double sumXX = 0.0;
	for (Point point : dataPoints) {
	sumX += point.x;
	sumXX += point.x * point.x;
	sumY += point.y;
	sumXY += point.x * point.y;
	}

	// a = (NΣXY - (ΣX)(ΣY)) / (NΣX² - (ΣX)²)
	final double a = (size * sumXY - sumX * sumY) / (size * sumXX - sumX * sumX);
	// b = (ΣY - b(ΣX)) / N
	final double b = (sumY - a * sumX) / size;

	List<Point> resultPoints = new ArrayList<Point>();
	for (Point point : dataPoints) {
	// y = ax + b
	resultPoints.add(new Point(point.x, a * point.x + b));
	}
	return resultPoints.toArray(new Point[resultPoints.size()]);
	}
	}