Javascript – Google Charts: compound chart with column and line chart

It took me a while, to figure this out, but Google Charts does support dual Y-axis (v-axis). I want to use the Javascript API and not the HTML interface.

This example can be tested here: http://code.google.com/apis/ajax/playground/?type=visualization#line_chart

Replace all of that code with this code showing how to have two different Y-axis scales:

function drawVisualization() {
  // Create and populate the data table.
  var data = new google.visualization.DataTable();
  data.addColumn('string', 'x');
  data.addColumn('number', 'Cats');
  data.addColumn('number', 'Blanket 1');
  data.addColumn('number', 'Blanket 2');
  data.addRow(["A", 1, 1, 0.5]);
  data.addRow(["B", 2, 0.5, 1]);
  data.addRow(["C", 4, 1, 0.5]);
  data.addRow(["D", 8, 0.5, 1]);
  data.addRow(["E", 7, 1, 0.5]);
  data.addRow(["F", 7, 0.5, 1]);
  data.addRow(["G", 8, 1, 0.5]);
  data.addRow(["H", 4, 0.5, 1]);
  data.addRow(["I", 2, 1, 0.5]);
  data.addRow(["J", 3.5, 0.5, 1]);
  data.addRow(["K", 3, 1, 0.5]);
  data.addRow(["L", 3.5, 0.5, 1]);
  data.addRow(["M", 1, 1, 0.5]);
  data.addRow(["N", 1, 0.5, 1]);


  // Create and draw the visualization.
  new google.visualization.LineChart(document.getElementById('visualization')).
      draw(data, {curveType: "function", width: 500, height: 400,
    vAxes: {0: {logScale: false},
            1: {logScale: false, maxValue: 2}},
    series:{
       0:{targetAxisIndex:0},
       1:{targetAxisIndex:1},
       2:{targetAxisIndex:1}}}
          );
}

By adding maxValue: 2 to the code, and setting series 1 & 2 to that axis, they work properly on a second axis.

In the Configuration Options of the chart, specify

backgroundColor: { fill:'transparent' }

This worked for me in Chrome and Firefox. It took me some time to find out. The doc page says you can only put in HTML color strings and I assumed 'transparent' was not one of them.