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jirapos...@reviews.apache.org commented on MAHOUT-923:
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Hm. I hope i did not read the code or miss something.
1 -- i am not sure this will actually work as intended unless # of reducers is
corced to 1, of which i see no mention in the code.
2 -- mappers do nothing, passing on all the row pressure to sort which is
absolutely not necessary. Even if you use combiners. This is going to be
especially the case if you coerce 1 reducer an no combiners. IMO mean
computation should be pushed up to mappers to avoid sort pressures of map
reduce. Then reduction becomes largely symbolical(but you do need pass on the #
of rows mapper has seen, to the reducer, in order for that operation to apply
correctly).
3 -- i am not sure -- is NullWritable as a key legit? In my experience sequence
file reader cannot instantiate it because NullWritable is a singleton and its
creation is prohibited by making constructor private.
- Dmitriy
On 2011-12-12 00:30:24, Raphael Cendrillon wrote:
bq.
bq. -----------------------------------------------------------
bq. This is an automatically generated e-mail. To reply, visit:
bq. https://reviews.apache.org/r/3147/
bq. -----------------------------------------------------------
bq.
bq. (Updated 2011-12-12 00:30:24)
bq.
bq.
bq. Review request for mahout.
bq.
bq.
bq. Summary
bq. -------
bq.
bq. Here's a patch with a simple job to calculate the row mean (column-wise
mean). One outstanding issue is the combiner, this requires a wrtiable class
IntVectorTupleWritable, where the Int stores the number of rows, and the Vector
stores the column-wise sum.
bq.
bq.
bq. This addresses bug MAHOUT-923.
bq. https://issues.apache.org/jira/browse/MAHOUT-923
bq.
bq.
bq. Diffs
bq. -----
bq.
bq.
/trunk/core/src/main/java/org/apache/mahout/math/hadoop/DistributedRowMatrix.java
1213095
bq.
/trunk/core/src/main/java/org/apache/mahout/math/hadoop/MatrixRowMeanJob.java
PRE-CREATION
bq.
/trunk/core/src/test/java/org/apache/mahout/math/hadoop/TestDistributedRowMatrix.java
1213095
bq.
bq. Diff: https://reviews.apache.org/r/3147/diff
bq.
bq.
bq. Testing
bq. -------
bq.
bq. Junit test
bq.
bq.
bq. Thanks,
bq.
bq. Raphael
bq.
bq.
> Row mean job for PCA
> --------------------
>
> Key: MAHOUT-923
> URL: https://issues.apache.org/jira/browse/MAHOUT-923
> Project: Mahout
> Issue Type: Improvement
> Components: Math
> Affects Versions: 0.6
> Reporter: Raphael Cendrillon
> Assignee: Raphael Cendrillon
> Fix For: Backlog
>
> Attachments: MAHOUT-923.patch
>
>
> Add map reduce job for calculating mean row (column-wise mean) of a
> Distributed Row Matrix for use in PCA.
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