@Carmen,

Based on your requirement it seems you are trying to render a chart corresponding to the options selected from a dropdown list. If so, please check this JSFiddle example.

You can update the chart options / data based on the options selected from dropdown list as shown below –

$( ".dropdown" ).change(function() {
    chart.options.data[0].dataPoints = [];
    var e = document.getElementById("dd");
    var selected = e.options[e.selectedIndex].value;
    dps = jsonData[selected];
    for(var i in dps) {
      var xVal = dps[i].x;
      chart.options.data[0].dataPoints.push({x: new Date(xVal), y: dps[i].y});
    }
  chart.render();
});

___________
Indranil Deo
Team CanvasJS