Github user takuti commented on the issue:
https://github.com/apache/incubator-hivemall/pull/108
I tested `each_top_k`, `to_ordered_map` and `to_ordered_list` on the same
MovieLens 1M data. As we expected, `to_ordered_map` collects duplicated keys,
and the number of ratings is 3 while we launched top-10 aggregation.
```sql
with topk as (
select
each_top_k(
10, userid, rating,
userid, movieid
) as (rank, rating, userid, movieid)
from (
select
userid, movieid, rating
from ratings
cluster by userid
) t
)
select
count(1), collect_list(array(movieid, rating))
from
topk
where
userid = 1
;
```
> 10
[[527.0,5.0],[3105.0,5.0],[1270.0,5.0],[48.0,5.0],[1035.0,5.0],[1193.0,5.0],[1287.0,5.0],[2355.0,5.0],[595.0,5.0],[2804.0,5.0]]
```sql
with topk as (
select
userid,
to_ordered_map(rating, movieid, 10) as movies
from
ratings
group by
userid
)
select
count(1), collect_list(array(movieid, rating))
from
topk
lateral view explode(movies) t as rating, movieid
where
userid = 1
;
```
> 3 [[2028,5],[1246,4],[745,3]]
```sql
with topk as (
select
userid,
to_ordered_list(movieid, rating, '-k 10') as movies
from
ratings
group by
userid
)
select
size(movies), movies
from
topk
where
userid = 1
;
```
> 10 [595,1035,3105,2355,1287,2804,1193,2028,1029,1270]
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