[jira] [Resolved] (MADLIB-978) Implement skipping of arrays-with-NULL for elastic net training

["Frank McQuillan (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MADLIB-978?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Frank McQuillan resolved MADLIB-978.
------------------------------------
    Resolution: Fixed

> Implement skipping of arrays-with-NULL for elastic net training
> ---------------------------------------------------------------
>
>                 Key: MADLIB-978
>                 URL: https://issues.apache.org/jira/browse/MADLIB-978
>             Project: Apache MADlib
>          Issue Type: Improvement
>          Components: Module: Regularized Regression
>            Reporter: Frank McQuillan
>            Priority: Minor
>             Fix For: v1.9.1
>
>
> This JIRA is related to 
> https://issues.apache.org/jira/browse/MADLIB-919
> for predict function
> Implement skipping of arrays-with-NULL for elastic net predict.  Some context for this JIRA is below…
> (Q)
> Question came in this week from a MADlib user:
> Function "madlib.elastic_net_gaussian_predict(double precision[],double precision,double precision[])": Error converting an array w/ NULL value    s to dense format. (UDF_impl.hpp:210)
> Is there a typical pattern for handling nulls in such a scenario, perhaps converting to 0.0 or something like this?
> (A)
> Answer:
> The skipping of arrays-with-NULL has not been implemented for elastic net predict yet.
> You can workaround it by creating the below function: 
> http://stackoverflow.com/questions/7819021/replace-null-values-in-an-array-in-postgresql
> CREATE OR REPLACE FUNCTION f_array_replace_null (double precision[], double precision)
> RETURNS double precision[] AS
> $$
> SELECT ARRAY (
> SELECT COALESCE(x, $2)
> FROM unnest($1) x);
> $$ LANGUAGE SQL IMMUTABLE;
> They'll have to add the function before the feature array in the elastic_net statement: 
> f_array_replace_null(array["pf_calc_fdy_position", ...], 0)
> This would replace each NULL with a 0. The downside is it could get slower since the unnest and nest would happen with each call. If performance is a concern, and if they're running over this data multiple times, I would create a new table with the NULLs replaced and execute elastic_net_xxx in the regular way.



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