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> Von: Najum Ali <naju...@googlemail.com> > Betreff: Confusion using Mahout Recommender Evaluation > Datum: 8. Mai 2014 12:44:01 MESZ > An: user@mahout.apache.org > > Hi, > > I have a question about using the > AverageAbsoluteDifferenceRecommenderEvaluator #evaluate method. > > Using a GenericUserBasedRecommender: > > new RecommenderBuilder() { > @Override > public Recommender buildRecommender(DataModel model) throws TasteException { > UserSimilarity userSimilarity = new PearsonCorrelationSimilarity(model); > UserNeighborhood userNeighborhood = new NearestNUserNeighborhood(50, > userSimilarity, model); > return new GenericUserBasedRecommender(model, userNeighborhood, > userSimilarity); > } > }; > > the AverageAbsoluteDifferenceRecommenderEvaluator prints this in the > beginning time: > > 12:02:04.000 [pool-1-thread-1] INFO > org.apache.mahout.cf.taste.impl.eval.StatsCallable - Average time per > recommendation: 127ms > 12:02:04.000 [pool-1-thread-1] INFO > org.apache.mahout.cf.taste.impl.eval.StatsCallable - Approximate memory used: > 826MB / 960MB > > And getting a recommendation with > recommenderBuilder.buildRecommender(model).recommend(101, 10); - takes about > 186.091 ms .. thats pretty much something like the average time per > recommendation from the AverageAbsoluteDifferenceRecommenderEvaluator > > > Now, with GenericItemBasedRecommender following happens: > > new RecommenderBuilder() { > @Override > public Recommender buildRecommender(DataModel model) throws TasteException { > ItemSimilarity itemSimilarity = new PearsonCorrelationSimilarity(model); > return new GenericItemBasedRecommender(model, itemSimilarity); > } > }; > > Evaluation Output: > 11:59:19.950 [main] INFO > o.a.m.c.t.i.eval.AbstractDifferenceRecommenderEvaluator - Starting timing of > 63493 tasks in 8 threads > 11:59:19.979 [pool-1-thread-1] INFO > org.apache.mahout.cf.taste.impl.eval.StatsCallable - Average time per > recommendation: 26ms > 11:59:19.979 [pool-1-thread-1] INFO > org.apache.mahout.cf.taste.impl.eval.StatsCallable - Approximate memory used: > 598MB / 897MB > > yea .. it´s every time something like 26ms > > But in fact, using this Recommender I have to wait a looong time for an > answer - recommenderBuilder.buildRecommender(model).recommend(101, 10); > > GenericItemBasedRecommender —> 49267.09 ms .. or sometimes less ...but never > and ever under 100ms !! > > I am using the GroupLens 10M data with GroupLensDataModel and the evaluation > I am using 0.95 trainingPercentage data and 1.0 evaluationPercentage > > With the full evaluationPercentage i will make sure that the recommendations > created, takes all items into account.. so I can compare the average > recommendation time with a normal recommendation > > Why is the average time per recommendation so less by using a > GenericItemBasedRecommender with > AverageAbsoluteDifferenceRecommenderEvaluator?? But in face it is not that > fast using the method #recommend > > I don´t get it .. hope someone clear this out !! Thanks!
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