How To Bar Chart

How To Create a Bar Chart

Here is a short example on how to create and display a bar chart.

The old and improvised way

// have some data
String[] cases = {"A","B","C","D1","D2*"};
double[] scores = IntStream.range(0, cases.length)
      .mapToDouble(i->Math.random()).toArray();
// make helper function to create the bars
BiFunction<Integer,Double,Triangles> makeBar = (row, val)->{
   Triangles bar = new Triangles();
   bar.addQuad(new Rectangle2D.Double(0, row-0.4, val, 0.8));
   bar.getTriangleDetails().forEach(tri->{
      int red=0xff_e41a1c, blue=0xff_377eb8;
      tri.setColor(val < 0.5 ? red:blue);
   });
   return bar;
};
// We want to display Triangles, so we need the appropriate renderer.
TrianglesRenderer barRenderer = new TrianglesRenderer();
// add the bar for each case to the renderer
for(int i=0; i<cases.length; i++){
   Triangles bar = makeBar.apply(i, scores[i]);
   barRenderer.addItemToRender(bar);
}
// use a coordinate system for display
CoordSysRenderer coordsys = new CoordSysRenderer();
coordsys.setCoordinateView(0, -1, 1, cases.length);
// set the content renderer of the coordinate system 
coordsys.setContent(barRenderer);
// we need to change the tick marks labeling for the y axis
TickMarkGenerator oldTickGen = coordsys.getTickMarkGenerator();
coordsys.setTickMarkGenerator((min,max,desired,vert)->{
   if(!vert){
      return oldTickGen.genTicksAndLabels(min,max,desired,vert);
   }
   // make ticks at integer values (0,1,2,...)
   double[] ticks = IntStream.range(0, cases.length)
         .mapToDouble(i -> (double)i)
         .toArray();
   // use case names as tick mark labels
   return Pair.of(ticks, cases);
});
// set axis labels
coordsys.setxAxisLabel("Score");
coordsys.setyAxisLabel("");

// display within a JFrame
JFrame frame = new JFrame();
boolean useOpenGL = true;
JPlotterCanvas canvas = useOpenGL ? new BlankCanvas() : new BlankCanvasFallback();
canvas.setRenderer(coordsys);
canvas.asComponent().setPreferredSize(new Dimension(500, 300));
canvas.asComponent().setBackground(Color.WHITE);
frame.getContentPane().add(canvas.asComponent());
frame.setTitle("barchart");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
canvas.addCleanupOnWindowClosingListener(frame);
// make visible on AWT event dispatch thread
SwingUtilities.invokeLater(()->{
   frame.pack();
   frame.setVisible(true);
});

The new way (using a dedicated class)

// have some data
String[] cases = {"A","B","C","D1","D2*"};
double[] scores = IntStream.range(0, cases.length)
   .mapToDouble(i->Math.random()).toArray();
DoubleFunction<Color> colormap =  (val) -> {
   int red=0xff_e41a1c, blue=0xff_377eb8;
   return val < 0.5 ? new Color(red):new Color(blue);
};

// make the barchart
BarChart barchart = new BarChart(true, AlignmentConstants.HORIZONTAL);
for(int i=0; i<cases.length; i++) {
   BarGroup group = new BarGroup();
   group.addBarStack(0, scores[i], colormap.apply(scores[i]), cases[i]);
   barchart.addData(group);
}
// only single bar per group, no need for gap
barchart.getBarRenderer().setBargroupGap(0);
// select view automatically to fit all bars
barchart.alignBarRenderer();
barchart.getBarRenderer().setxAxisLabel("Score");

// boilerplate code to put the component in a frame and show it
JFrame frame = new JFrame();
barchart.getCanvas().asComponent().setPreferredSize(new Dimension(500, 300));
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(barchart.getCanvas().asComponent());
SwingUtilities.invokeLater(()->{
   frame.pack();
   frame.setVisible(true);
});

The BarChart class is quite versatile, it can also group and stack bars. Here is an example: