javascript - All series on a given axis must be of the same data type for line chart -

i'm working on line chart using google js , have given sample values testing , i'm getting error

all series on given axis must of same data type 

script

 function drawchart() {             // var data = google.visualization.arraytodatatable(chartdata);             var data = new google.visualization.datatable();             data.addcolumn('number', 'year');             data.addcolumn('string', 'value');             data.addcolumn('number', 'quantity');             data.addrows([                            [2008,'value1',36],                            [2009,'value2',27],                            [2010,'value3',39]             ]);             var options = {                 title: "company performance product category wise",                 pointsize: 5             };             var linechart = new google.visualization.linechart(document.getelementbyid('chart_div'));             linechart.draw(data, options);         } 

html

 <div id="chart_div" style="width: 600px; height: 400px">         </div> 

works fine 2 columns...

data.addcolumn('string', 'year'); data.addcolumn('number', 'quantity'); data.addrows([  ['2008',36],  ['2009',27],  ['2010',39] ]);