Pig: Get top n values per group

Question

I have data that's already grouped and aggregated, it looks like so:

user    value      count
----    --------  ------
Alice   third      5
Alice   first      11
Alice   second     10
Alice   fourth     2
...
Bob     second     20
Bob     third      18
Bob     first      21
Bob     fourth     8
...

For every user (Alice and Bob), I want retrieve their top n values (let's say 2), sorted terms of 'count'. So the desired output I want is this:

Alice first 11
Alice second 10
Bob first 21
Bob second 20

How can I accomplish that?

Answer 1

One approach is

records = LOAD '/user/nubes/ncdc/micro-tab/top.txt' AS (user:chararray,value:chararray,counter:int);
grpd = GROUP records BY user;

top3 = foreach grpd {
        sorted = order records by counter desc;
        top    = limit sorted 2;
        generate group, flatten(top);
};

Input is:

Alice   third   5 
Alice   first   11 
Alice   second  10
Alice   fourth  2
Bob second  20
Bob third   18
Bob first   21
Bob fourth  8

Output is:

(Alice,Alice,first,11)
(Alice,Alice,second,10
(Bob,Bob,first,21)
(Bob,Bob,second,20)