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From "Michael Haeusler (JIRA)" <>
Subject [jira] [Created] (HIVE-11022) Support collecting lists in user defined order
Date Tue, 16 Jun 2015 16:25:00 GMT
Michael Haeusler created HIVE-11022:

             Summary: Support collecting lists in user defined order
                 Key: HIVE-11022
             Project: Hive
          Issue Type: New Feature
          Components: UDF
            Reporter: Michael Haeusler

Hive currently supports aggregation of lists "in order of input rows" with the UDF collect_list.
Unfortunately, the order is not well defined when map-side aggregations are used.

Hive could support collecting lists in user-defined order by providing a UDF
COLLECT_LIST_SORTED(valueColumn, sortColumn[, limit]), that would return a list of values
sorted in a user defined order. An optional limit parameter can restrict this to the n first
values within that order.

Especially in the limit case, this can be efficiently pre-aggregated and reduce the amount
of data transferred to reducers.

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