js 根据数组分组动态生成table（相同项合并）

<!doctype html public "-//w3c//dtd html 4.01 transitional//en" "http://www.w3.org/tr/html4/loose.dtd">
<html>
<head>
<title> new document </title>
<script>
//xxbh:学校编号，bjbh:班级编号,xx：姓名
var arrjson=[
{'xxbh':'1001','bjbh':'0801','xx':'李四'},{'xxbh':'1001','bjbh':'0802','xx':'张三'},
{'xxbh':'1003','bjbh':'0803','xx':'王五'},{'xxbh':'1003','bjbh':'0804','xx':'晶晶'},
{'xxbh':'1005','bjbh':'0701','xx':'亮亮'},{'xxbh':'1002','bjbh':'0701','xx':'明敏'},
{'xxbh':'1005','bjbh':'0701','xx':'张灿'},{'xxbh':'1002','bjbh':'0801','xx':'小白'},
{'xxbh':'1005','bjbh':'0802','xx':'小胖'},{'xxbh':'1002','bjbh':'0901','xx':'小丽'},
{'xxbh':'1003','bjbh':'0901','xx':'阿宝'},{'xxbh':'1004','bjbh':'0901','xx':'王泰'},
{'xxbh':'1001','bjbh':'0901','xx':'阿毛'},{'xxbh':'1006','bjbh':'0901','xx':'李铭'},
{'xxbh':'1005','bjbh':'0901','xx':'阿城'},{'xxbh':'1004','bjbh':'0901','xx':'张晓'},
{'xxbh':'1006','bjbh':'0901','xx':'小小'},{'xxbh':'1004','bjbh':'0901','xx':'白昼'},
{'xxbh':'1002','bjbh':'0901','xx':'乐乐'},{'xxbh':'1001','bjbh':'0901','xx':'黎明'}
];
function creatmapbyxxbh(arrjson){
var xxbhmap={};
var len = arrjson.length;
for(var i=0;i<len;i++){

if(xxbhmap[arrjson[i].xxbh] == undefined){
var list = [];
list.push(arrjson[i]);
xxbhmap[arrjson[i].xxbh] = list;
}else{
xxbhmap[arrjson[i].xxbh].push(arrjson[i]);
}

}
var str="<table border='1'><tr><td width='200'>学校编号</td><td width='200'>班级</td><td width='200'>姓名</td></tr>";
for(var xxbh in xxbhmap){
var stu = xxbhmap[xxbh];
alert(stu.length);
str+="<tr><td rowspan='"+stu.length+"'>"+xxbh+"</td>";
for(var i = 0;i < stu.length;i++){
//document.write(xxbh + " "+stu[i].bjbh+" "+stu[i].xx +"<br />")
//document.write("<table><tr><td>学校编号</td><td>班级</td><td>姓名</td></tr></table> ")
if(i==0){
str+="<td>"+stu[i].bjbh+"</td><td>"+stu[i].xx+"</td></tr>";
}else{
str+="<tr><td>"+stu[i].bjbh+"</td><td>"+stu[i].xx+"</td></tr>";
}
}
str+="<tr ><td colspan='3'>"+xxbh+"共有"+stu.length+"个班级</td></tr>"
}
str+="</table> ";
document.write(str)
}
</script>
</head >
<body>
<button onclick='creatmapbyxxbh(arrjson)'>测试</button>
</body>
</html>