[jira] Resolved: (MAHOUT-162) Added support for mapping String to long IDs in CF code

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

     [ https://issues.apache.org/jira/browse/MAHOUT-162?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sean Owen resolved MAHOUT-162.
------------------------------

    Resolution: Fixed

Committed patch as it seems to work for me (and Otis I presume) and heard no objections.

> Added support for mapping String to long IDs in CF code
> -------------------------------------------------------
>
>                 Key: MAHOUT-162
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-162
>             Project: Mahout
>          Issue Type: Improvement
>          Components: Collaborative Filtering
>    Affects Versions: 0.2
>            Reporter: Sean Owen
>            Assignee: Sean Owen
>             Fix For: 0.2
>
>         Attachments: MAHOUT-162.patch
>
>
> Since the framework now only allows long (64-bit integer) IDs, and no longer Strings, we need to provide some support for translating between the two. The basic proposal is this:
> - Define a one-way mapping from Strings to longs that is repeatable and easy to implement in many contexts. In particular I propose using the bottom 64 bits of the MD5 hash of a string.
> - Define support for storing the reverse mapping (longs to Strings) in various ways, in an efficient way, that handles gracefully the very rare possibility of collision

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