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https://issues.apache.org/jira/browse/FLINK-4613?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15532473#comment-15532473
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ASF GitHub Bot commented on FLINK-4613:
---------------------------------------

Github user gaborhermann commented on a diff in the pull request:

    https://github.com/apache/flink/pull/2542#discussion_r81112526
  
    --- Diff: docs/dev/libs/ml/als.md ---
    @@ -99,6 +114,26 @@ The alternating least squares implementation can be 
controlled by the following
             </td>
           </tr>
           <tr>
    +        <td><strong>ImplicitPrefs</strong></td>
    +        <td>
    +          <p>
    +            Implicit property of the observations, meaning that they do 
not represent an explicit
    +            preference of the user, just the implicit information how many 
times the user consumed the
    --- End diff --
    
    Thanks. Fixed.


> Extend ALS to handle implicit feedback datasets
> -----------------------------------------------
>
>                 Key: FLINK-4613
>                 URL: https://issues.apache.org/jira/browse/FLINK-4613
>             Project: Flink
>          Issue Type: New Feature
>          Components: Machine Learning Library
>            Reporter: Gábor Hermann
>            Assignee: Gábor Hermann
>
> The Alternating Least Squares implementation should be extended to handle 
> _implicit feedback_ datasets. These datasets do not contain explicit ratings 
> by users, they are rather built by collecting user behavior (e.g. user 
> listened to artist X for Y minutes), and they require a slightly different 
> optimization objective. See details by [Hu et 
> al|http://dx.doi.org/10.1109/ICDM.2008.22].
> We do not need to modify much in the original ALS algorithm. See [Spark ALS 
> implementation|https://github.com/apache/spark/blob/master/mllib/src/main/scala/org/apache/spark/ml/recommendation/ALS.scala],
>  which could be a basis for this extension. Only the updating factor part is 
> modified, and most of the changes are in the local parts of the algorithm 
> (i.e. UDFs). In fact, the only modification that is not local, is 
> precomputing a matrix product Y^T * Y and broadcasting it to all the nodes, 
> which we can do with broadcast DataSets. 



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