如何在c3js饼图上绘制定制的JSON数据?

JSON看起来像这样(这是动态数据):

{"ug":["K","M2","M3","M4"],"wtv":[10,20,35,60]}

HTML:

<div id="chart"></div>

JS(我实际尝试的):

var json ={"ug":["K","M2","M3","M4"],"wtv":[10,20,35,60]};
var ug =json.ug;
var wtv=json.wtv;     
var chart = c3.generate({
    data: {
       json: {
          ug:wtv[0],
          ug1:wtv[1],
          ug2:wtv[2],
          ug3:wtv[3],
        },
        type : 'pie',
    }
});

Here is a fiddle for reference.

有人能帮我根据需要操作数据来绘制饼图吗?