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From "Christoph Nagel (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAHOUT-747) Entropy implementation in Map/Reduce
Date Wed, 06 Jul 2011 15:05:16 GMT

    [ https://issues.apache.org/jira/browse/MAHOUT-747?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13060624#comment-13060624
] 

Christoph Nagel commented on MAHOUT-747:
----------------------------------------

Cool & Thanks. Looked at it and only one question.
Isn't *.common.mapreduce the best package for DoubleSumReducer, KeyCounterMapper, ValueCounterMapper,
VarInSumReducer? These are generic mapper and reducer and while coding, I was surprised, that
nobody had implemented them yet.

Regards, Christoph.

> Entropy implementation in Map/Reduce
> ------------------------------------
>
>                 Key: MAHOUT-747
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-747
>             Project: Mahout
>          Issue Type: New Feature
>          Components: Math
>    Affects Versions: 0.6
>            Reporter: Christoph Nagel
>            Assignee: Sean Owen
>             Fix For: 0.6
>
>         Attachments: MAHOUT-747.patch
>
>
> Hi again,
> because I got much to work with entropy and information gain ratio, I want to implement
the following distributed algorithms:
> * Entropy (https://secure.wikimedia.org/wikipedia/en/wiki/Entropy_%28information_theory%29)
> * Conditional Entropy (https://secure.wikimedia.org/wikipedia/en/wiki/Conditional_entropy)
> * Information Gain
> * Information Gain Ratio (https://secure.wikimedia.org/wikipedia/en/wiki/Information_gain_ratio)
> This issue is at first only for entropy.
> Some questions:
> * In which package do the classes belong. I put them first at 'org.apache.mahout.math.stats',
don't know if this is right, because they are components of information retrieval.
> * Entropy only reads a set of elements. As input i took a sequence file with keys of
type Text and values anyone, because I only work with the keys. Is this the best practise?
> * Is there a generic solution, so that the type of keys can be anything inherited from
Writable?
> In Hadoop is a TokenCounterMapper, which emits each value with an IntWritable(1). I added
a KeyCounterMapper into 'org.apache.mahout.common.mapreduce' which does the same with the
keys.
> Will append my patch soon.
> Regards, Christoph.

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