Hive: Is there a better way to percentile rank a column?

Question

Currently, to percentile rank a column in hive, I am using something like the following. I am trying to rank items in a column by what percentile they fall under, assigning a value form 0 to 1 to each item. The code below assigns a value from 0 to 9, essentially saying that an item with a char_percentile_rank of 0 is in the bottom 10% of items, and a value of 9 is in the top 10% of items. Is there a better way of doing this?

select item
    , characteristic
    , case when characteristic <= char_perc[0] then 0
        when characteristic <= char_perc[1] then 1
        when characteristic <= char_perc[2] then 2
        when characteristic <= char_perc[3] then 3
        when characteristic <= char_perc[4] then 4
        when characteristic <= char_perc[5] then 5
        when characteristic <= char_perc[6] then 6
        when characteristic <= char_perc[7] then 7
        when characteristic <= char_perc[8] then 8
        else 9
      end as char_percentile_rank
from (
    select split(item_id,'-')[0] as item
        , split(item_id,'-')[1] as characteristic
        , char_perc
    from (
        select collect_set(concat_ws('-',item,characteristic)) as item_set
            , PERCENTILE(BIGINT(characteristic),array(0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9)) as char_perc
        from(
            select item
                , sum(characteristic) as characteristic
            from table
            group by item
        ) t1
    ) t2
    lateral view explode(item_set) explodetable as item_id
) t3

Note: I had to do the collect_set in order to avoid a self join, as the percentile function implicitly performs a group by.

I've gathered that the percentile function is horribly slow (at least in this usage). Perhaps it would be better to manually calculate percentile?

Answer 1

Try removing one of your derived tables

select item
    , characteristic
    , case when characteristic <= char_perc[0] then 0
        when characteristic <= char_perc[1] then 1
        when characteristic <= char_perc[2] then 2
        when characteristic <= char_perc[3] then 3
        when characteristic <= char_perc[4] then 4
        when characteristic <= char_perc[5] then 5
        when characteristic <= char_perc[6] then 6
        when characteristic <= char_perc[7] then 7
        when characteristic <= char_perc[8] then 8
        else 9
      end as char_percentile_rank
from (
     select item, characteristic,
         , PERCENTILE(BIGINT(characteristic),array(0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9)) over () as char_perc 
     from (
       select item
         , sum(characteristic) as characteristic             
       from table
       group by item            
     ) t1
) t2