[jira] Commented: (SOLR-680) StatsComponent - get min, max, sum, qt, avg of number fields

["Sean Timm (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SOLR-680?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12635752#action_12635752 ] 

Sean Timm commented on SOLR-680:
--------------------------------

Ryan--

If you want to get the standard deviation with out a second pass, I think you can do it by additionally keeping the running sum of squares of the values.  Then:

{code}
    /**
     * Returns the standard deviation of all previously counted
     * values.  
     */
    public double standardDeviation()
    {
        if( _count <= 1.0D ) return 0.0D;
        return Math.sqrt( ( ( count * sumOfSquares ) - ( sum * sum ) )
                          / ( count * ( count - 1.0D ) ) );    
    
    }
{code}

> StatsComponent - get min, max, sum, qt, avg of number fields
> ------------------------------------------------------------
>
>                 Key: SOLR-680
>                 URL: https://issues.apache.org/jira/browse/SOLR-680
>             Project: Solr
>          Issue Type: New Feature
>          Components: search
>            Reporter: Koji Sekiguchi
>            Priority: Minor
>             Fix For: 1.4
>
>         Attachments: SOLR-680.patch, SOLR-680.patch, SOLR-680.patch, SOLR-680.patch
>
>
> StatsComponent - it returns min,max,sum,qt,avg of specified number fields:
> request parameters:
> &stats=on&stats.field=price
> {code:xml}
> <stats>
>  <stats_fields>
>    <lst name="price">
>        <double name="min">10</double>
>        <double name="max">30</double>
>        <double name="avg">20</double>
>        <double name="sum">60</double>
>        <double name="qt">3</double>
>    </lst>
>  </stats_fields>
> </stats>
> {code}
> WRT "stats", the component can output sum and avg, but not sd and var.
> USE CASE:
> StatsComponent can be used to get "market price" of DocSet e.g. rental housing site, package tour site.

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