根据后台返回数据条数进行pie图radius定位；
 
 
var a = 100;
var b = 0;
var c = 0;
var radius = [];
for (var i in data) {
a = a - 15;
 b = a - 5;
if (a < 0) { break;}
 radius.push([a + '%', b + '%']);
}