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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: > > ----------------------------------------------------------- > This is an automatically generated e-mail. To reply, visit: > https://reviews.apache.org/r/3147/ > ----------------------------------------------------------- > > (Updated 2011-12-12 00:30:24) > > > Review request for mahout. > > > Summary > ------- > > 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. > > > This addresses bug MAHOUT-923. > https://issues.apache.org/jira/browse/MAHOUT-923 > > > Diffs > ----- > > > /trunk/core/src/main/java/org/apache/mahout/math/hadoop/DistributedRowMatrix.java > 1213095 > > /trunk/core/src/main/java/org/apache/mahout/math/hadoop/MatrixRowMeanJob.java > PRE-CREATION > > /trunk/core/src/test/java/org/apache/mahout/math/hadoop/TestDistributedRowMatrix.java > 1213095 > > Diff: https://reviews.apache.org/r/3147/diff > > > Testing > ------- > > Junit test > > > Thanks, > > Raphael > >
