[jira] Commented: (MAHOUT-322) DistributedRowMatrix should live in SequenceFile instead of SequenceFile

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

    [ https://issues.apache.org/jira/browse/MAHOUT-322?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12914947#action_12914947 ] 

Sean Owen commented on MAHOUT-322:
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Is this issue still live? I'm guessing it's either already fixed or a de facto wont-fix.

> DistributedRowMatrix should live in SequenceFile<Writable,VectorWritable> instead of SequenceFile<IntWritable,VectorWritable>
> -----------------------------------------------------------------------------------------------------------------------------
>
>                 Key: MAHOUT-322
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-322
>             Project: Mahout
>          Issue Type: Improvement
>          Components: Math
>    Affects Versions: 0.3
>            Reporter: Danny Leshem
>            Priority: Minor
>
> Class documentation for org.apache.mahout.math.hadoop.DistributedRowMatrix states that the matrix lives in SequenceFile<WritableComparable, VectorWritable>. Implementation, however, assumes SequenceFile<IntWritable, VectorWritable> is passed.
> Currently, usage of this class inside Mahout is limited to Jake Mannix's SVD package, mainly to perform PCA on a massive document corpus. Given such corpus, it makes sense to not limit the user by forcing the document "key" to be integer. Instead, users should be able to use Text keys (document name or id) or keys made of any other arbitrary class. One may even argue that forcing a WritableComparable key is too limiting, and a simple Writable key should be assumed.
> In fact, it would be best if DistributedRowMatrix did not read the SequenceFile key at all, to allow user-specific classes (unknown to Mahout) to be used as opaque keys even when their libraries are not available in runtime. Currently DistributedRowMatrix calls "reader.next(i, v)"... but reader has methods to query just the value, avoiding key deserialization altogether.

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