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From "Robin Anil (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAHOUT-322) DistributedRowMatrix should live in SequenceFile<Writable,VectorWritable> instead of SequenceFile<IntWritable,VectorWritable>
Date Thu, 04 Mar 2010 17:35:27 GMT

    [ https://issues.apache.org/jira/browse/MAHOUT-322?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12841397#action_12841397
] 

Robin Anil commented on MAHOUT-322:
-----------------------------------

take a look at MeanShiftCanopyCreatorMapper. This is a fast form of assigning ids to records
but aren't continuous.  This way, It is scalable 

> 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
>             Fix For: 0.3
>
>
> 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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