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