mapreduce 求教

[cshiqin]

db.class.insert({class:1,student:1,subject :1,score:90 });
db.class.insert({class:1,student:1,subject :2,score:90 });
db.class.insert({class:1,student:1,subject :3,score:90 });
db.class.insert({class:1,student:2,subject :1,score:90 });
db.class.insert({class:1,student:2,subject :2,score:90 });
db.class.insert({class:1,student:2,subject :3,score:90 });
db.class.insert({class:2,student:1,subject :1,score:90 });
db.class.insert({class:2,student:1,subject :2,score:90 });
db.class.insert({class:2,student:1,subject :3,score:90 });
db.class.insert({class:2,student:2,subject :1,score:90 });
db.class.insert({class:2,student:2,subject :2,score:90 });
db.class.insert({class:2,student:2,subject :3,score:90 });

如何用mapreduce写每个班的每个科目的总分?
就是相当于sql中的
select class,subject,sum(score) from class group by class,subject;
mapreduce是不是只能求每个班的总分,或每个科目的总分呀?
就是

[cshiqin]

没人回复,自己顶一下.

[cshiqin]

谢谢,你这是group by class 我要的是group by class,subject

[cshiqin]

引用 3 楼 fengyun4hao 的回复:

GroupBy groupby=new GroupBy("function(doc){ return{'class':doc.class,true}; }") groupby.initialDocument("{total:0}"); groupby.reducefunction("function(doc,p……

谢谢,你这是group by class 我要的是group by class,subject

[cshiqin]

没人回复,自己顶一下.

[fengyun4hao]

GroupBy groupby=new GroupBy("function(doc){ return{'class':doc.class,true}; }") groupby.initialDocument("{total:0}"); groupby.reducefunction("function(doc,prev){ prev.total++; }") 在java程序中写的，用到了mongo的jar包

[黄瓜黄瓜]

可以统计每个班的人数，每个班的每个人的总成绩 你想要的统计 都可以的 不用mapreduce 用aggregate 里面有 $group $max $min $avg $sum