How to add another data series to a Google chart

Question

I have setup a simple Google Chart by following the example on this page: http://code.google.com/apis/chart/interactive/docs/gallery/linechart.html

 google.load("visualization", "1", {packages:["corechart"]});
      google.setOnLoadCallback(drawChart);
      function drawChart() {
        var data = new google.visualization.DataTable();
        data.addColumn('string', 'Year');
        data.addColumn('number', 'Sales');
        data.addColumn('number', 'Expenses');
        data.addRows([
        ['2004', 1000, 400],
        ['2005', 1170, 460],
        ['2006',  860, 580],
        ['2007', 1030, 540]
        ]);

        var options = {
          width: 400, height: 240,
          title: 'Company Performance'
        };

        var chart = new google.visualization.LineChart(document.getElementById('chart_div'));
        chart.draw(data, options);
      }

But now, after it's rendered, with some javascript i want to dynamically add another series of data. Can anyone point me in the right direction on how to do this?
The data i want to add, a number column with the number of employees, should show a new line in the chart, in another color and doesn't start at year 2004 but at 2005,

Solution

You need to add new data to 'data' variable and call the chart.draw() method again. See the DataTable docs or play a bit at http://code.google.com/apis/ajax/playground/?type=visualization#line_chart

Example:

  // Add columns
  data.addColumn('string', 'Employee Name');
  data.addColumn('date', 'Start Date');

  // Add empty rows
  data.addRows(6);
  data.setCell(0, 0, 'Mike');
  data.setCell(0, 1, {v:new Date(2008,1,28), f:'February 28, 2008'});
  data.setCell(1, 0, 'Bob');
  data.setCell(1, 1, new Date(2007, 5, 1));
  data.setCell(2, 0, 'Alice');
  data.setCell(2, 1, new Date(2006, 7, 16));
  data.setCell(3, 0, 'Frank');
  data.setCell(3, 1, new Date(2007, 11, 28));
  data.setCell(4, 0, 'Floyd');
  data.setCell(4, 1, new Date(2005, 3, 13));
  data.setCell(5, 0, 'Fritz');
  data.setCell(5, 1, new Date(2007, 9, 2));

Comments

[Tys]

Is there a way to add the new data, without altering the original array? The problem with the above suggestion is that i first have to 'fit' the new data into that array. I could do that, but it doesn't really fit by default. Therefore my question..

[acanimal]

See the DataTable docs. You have the addColum and setCell methods. addColum to add a new serie and with setCell you can fill it.Also it is a good idea to hold a copy of your data in a variable different than the format required by the library you use. This way you can add more data to your source array and pass again to the visual library.

[Tys]

I was hoping for something more flexible, but i did it this way for now.