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https://issues.apache.org/jira/browse/IMPALA-10019?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Gabor Kaszab closed IMPALA-10019.
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Fix Version/s: Impala 4.0
Resolution: Fixed
> Implement ds_kll_pmf() function
> -------------------------------
>
> Key: IMPALA-10019
> URL: https://issues.apache.org/jira/browse/IMPALA-10019
> Project: IMPALA
> Issue Type: New Feature
> Reporter: Gabor Kaszab
> Assignee: Gabor Kaszab
> Priority: Major
> Fix For: Impala 4.0
>
>
> Requirements for ds_kll_pmf() (Probability Mass Function):
> - Receives a serialized KLL sketch in BINARY type (in Impala it can be
> STRING as long as we don't have BINARY) as first parameter.
> - Receives one or more float values to create ranges from the sketched data.
> - In Hive the return type is an array of doubles. However, Impala can't
> return complex types from functions at this point so we have to find some
> alternative approaches to implement this function. Follow whatever solution
> came up in https://issues.apache.org/jira/browse/IMPALA-9962
> An example:
> {code:java}
> select ds_kll_pmf(sketch_col, 1, 2, 3, 4) from sketches_table;
> {code}
> This will generate the following ranges: (-inf, 1), [1,2), [2,3), [3,4),
> [4,+inf)
> In Hive, the result would have an array of 5 doubles for the 5 ranges, where
> each number gives the probability between [0,1] that an item will fall into
> the particular range. Or in other words a ratio of items belonging to that
> range.
> Taking input values such as: 1,2,3,4,5
> {code:java}
> select ds_kll_pmf(f, 1, 3, 4, 5, 10) from kll_sketches;
> +----------------------------+
> | _c0 |
> +----------------------------+
> | [0.0,0.4,0.2,0.2,0.2,0.0] |
> +----------------------------+
> {code}
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