In general, workflows with matrices in Mahout handle SequenceFile<IntWritable, VectorWritable>, as this is the on-disk format of the class DistributedRowMatrix. The original Mahout LDA pre-dated this move to standardize closer to that format, and so it didn't have that requirement.
Now, as you say, it's true that in the new implementation, the keys aren't actually used, so in principle we could just go with WritableComparable<?> in CVB0Driver's mappers/reducers keys. In fact, it would make certain integrations a little nicer, at the cost of pushing incompatibility somewhere else. For example, the output p(document | topic) distributions go into a SequenceFile whose keys are the same as the input corpus keys (ie the doc_id values), and there may be workflows which take this matrix and transpose it to multiply it by another matrix or somethign of that nature. If the keys are IntWritable, this all works just fine. If not, then transpose will fail horribly, as will matrix multiplication. Standardizing on a common fixed format internally avoids some of these problems, while at the same time being a bit inflexible. It's possible we could add a command-line option + some internal switches to allow the user to explicitly force untyped keys, or just warn on non-integer keys or something... I can just imagine seeing the questions on this very list when someone takes the output of their Long-keyed corpus and try to matrix multiply it by some other matrix... -jake On Tue, Jan 24, 2012 at 1:27 PM, John Conwell <[email protected]> wrote: > I wanted to compare the two LDA implementations, and I noticed that for the > input corpus sequence file file (key: doc_id, value: vector), the Key for > the input file for LDADriver takes any WritableComparable<?> key, but the > Key for the input file for CVB0Driver requires IntWritable explicitly. Is > there some reason these two LDA implementations cant both use > WritableComparable<?> for the key of the input sequence file? It would > make integrating them into application workflows much easier and > consistant. > > -- > > Thanks, > John C >
