[jira] [Commented] (SOLR-6354) Support stats over functions

["Hoss Man (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SOLR-6354?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14091545#comment-14091545 ] 

Hoss Man commented on SOLR-6354:
--------------------------------


Proposed implementation...

* SimpleStats should check the local params of each {{stats.field}} for a "type" param 
** type is already treated special in local param parsing as as way to specify the parser type for the body of the string, ie: {{\{!foo\}...}} is just an alias for {{\{!type=foo\}...}}
* if "type" param doesn't exist, or is the empty string, treat the param value as a regular field name and get it's value source (just like is done today)
* if "type" does exist, do normal QParserPlugin lookup to parse the param value
** if the resulting Query is {{instanceof FunctionQuery}}, cast it and pull out it's ValueSource
** else: wrap the Query in a QueryValueSource
* add a new subclass of NumericStatsValues that can be constructed directly with a ValueSource



> Support stats over functions
> ----------------------------
>
>                 Key: SOLR-6354
>                 URL: https://issues.apache.org/jira/browse/SOLR-6354
>             Project: Solr
>          Issue Type: Sub-task
>            Reporter: Hoss Man
>
> The majority of the logic in StatsValuesFactory for dealing with stats over fields just uses the ValueSource API.  There's very little reason we can't generalize this to support computing aggregate stats over any arbitrary function (or the scores from an arbitrary query).
> Example...
> {noformat}
> stats.field={!func key=mean_rating mean=true}prod(user_rating,pow(editor_rating,2))
> {noformat}
> ...would mean that we can compute a conceptual "rating" for each doc by multiplying the user_rating field by the square of the editor_rating field, and then we'd compute the mean of that "rating" across all docs in the set and return it as "mean_rating"



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