可以在列组之前添加两列吗？ （谷歌图表）

Question

可以在列组之前添加两列吗？

这个图像是当前的情况，我会在列之前添加两列（GROUP＃1 GROUP＃2）。例如，参与者的一个类别列和列名称。

我没有在文档Google Charts中找到怎么做：https://developers.google.com/chart/interactive/docs/gallery/timeline?hl=pt

我的例子： http://jsfiddle.net/asgallant/7A88H/

Ex：现状：

Ex：所需输出的图像

代码当前情况。

function drawChart() {
    var container = document.getElementById('example4.2');
    var chart = new google.visualization.Timeline(container);
    var dataTable = new google.visualization.DataTable();
    
    dataTable.addColumn({ type: 'string', id: 'Group' });
    dataTable.addColumn({ type: 'string', id: 'Category' });
    dataTable.addColumn({ type: 'string', id: 'ID' });
    dataTable.addColumn({ type: 'date', id: 'Start' });
    dataTable.addColumn({ type: 'date', id: 'End' });
    dataTable.addRows([
        [ 'GROUP #1', 'CategoryA', 'C00001', new Date(2014, 0, 1), new Date(2014, 0, 31) ],
        [ 'GROUP #1', 'CategoryA', 'C00002', new Date(2014, 1, 1), new Date(2014, 1, 28) ],
        [ 'GROUP #1', 'CategoryA', 'C00003', new Date(2014, 3, 1),  new Date(2014, 3, 15) ],
        [ 'GROUP #1', 'CategoryB', 'C00003', new Date(2014, 0, 21),  new Date(2014, 2, 19) ],
        [ 'GROUP #1', 'CategoryA', 'C00004', new Date(2014, 0, 1),  new Date(2014, 0, 15) ],
        [ 'GROUP #2', 'CategoryC', 'C00005', new Date(2014, 2, 8),  new Date(2014, 2, 15) ],
        [ 'GROUP #3', 'CategoryC', 'C00006', new Date(2014, 5, 1),  new Date(2014, 5, 15) ],
        [ 'GROUP #4', 'CategoryA', 'C00007', new Date(2014, 1, 15),  new Date(2014, 1, 25) ]
    ]);
    
    var colors = [];
    var colorMap = {
        // should contain a map of category -> color for every category
        CategoryA: '#e63b6f',
        CategoryB: '#19c362',
        CategoryC: '#592df7'
    }
    for (var i = 0; i < dataTable.getNumberOfRows(); i++) {
        colors.push(colorMap[dataTable.getValue(i, 1)]);
    }
    
    var rowHeight = 41;
    var chartHeight = (dataTable.getNumberOfRows() + 1) * rowHeight;
    
    var options = {
        timeline: { 
            groupByRowLabel: true,
            rowLabelStyle: {
                fontName: 'Roboto Condensed',
                fontSize: 14,
                color: '#333333'
            },
            barLabelStyle: {
                fontName: 'Roboto Condensed',
                fontSize: 14
            }
        },                          
        avoidOverlappingGridLines: true,
        height: chartHeight,
        width: '100%',
        colors: colors
    };
    
    // use a DataView to hide the category column from the Timeline
    var view = new google.visualization.DataView(dataTable);
    view.setColumns([0, 2, 3, 4]);
    
    chart.draw(view, options);
}
google.load('visualization', '1', {packages:['timeline'], callback: drawChart});