Hadoop 计算FOREACH中的和

假设我有以下几点

DATA = foreach INPUT {
   //..
   generate group, count(name) as total;
}

我将以一个键按名称分组的关系结束

('mike', 'someprop', 10)
('mike', 'otherprop', 3)
('doug', 'xprop', 5)
...

我想得到每个名字前10名的总和：

ALIAS = group DATA by name;
RESULT = foreach ALIAS {
   SORTED = ORDER DATA by total desc;
   TOP10 = LIMIT SORTED 10;

   //doesn't work! can't have GROUP inside FOREACH
   AGG = group TOP10 ALL;
   TOPTOTAL = foreach AGG generate SUM(AGG.total);

   generate group, TOPTOTAL;
}

---

如何计算

foreach

中关系的值（总和、计数等）？目前无法在foreach中应用

分组ALL

。

SUM

只是一个以包为参数的函数，您可以通过从

TOP10

投影来创建此包：

ALIAS = group DATA by name;
RESULT = foreach ALIAS {
   SORTED = ORDER DATA by total desc;
   TOP10 = LIMIT SORTED 10;
   generate group, SUM(TOP10.total);
}