关于echarts画图，当Y轴设置为category，在series选择了状态，但不显示图像

Question

option = {

title : {
    text: '司机驾驶状态',
    subtext: '实时'
},
tooltip : {
    trigger: 'axis'
},
legend: {
    data:['状态']
},
toolbox: {},
calculable : true,
xAxis : [
    {
        type : 'category',
        boundaryGap : false,
        data : ['12:00','12:01','12:02','12:03','12:04','12:05','12:06','12:07','12:08','12:09','12:10','12:11']
    }
],
yAxis : [
    {
      type : 'category',
        boundaryGap : false,
        data:['清醒','疲劳','非常疲劳']
    }
],
series : [
    {
        name:'状态',
        type:'line',
        smooth:true,
        itemStyle: {normal: {areaStyle: {type: 'default'}}},
        data:['疲劳','清醒','清醒','清醒','疲劳','非常疲劳','疲劳','清醒','清醒','清醒','清醒','疲劳']
    },
]

};
这是代码，附上图像

为何没有状态的图

Answer 1

y轴应为数值