DistributedRowMatrix should live in SequenceFile<Writable,VectorWritable>
instead of SequenceFile<IntWritable,VectorWritable>
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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 the 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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