I am following the code example as below:
RandomUtils.useTestSeed();
DataModel model = new FileDataModel(new File(file));
RecommenderIRStatsEvaluator evaluator = new GenericRecommenderIRStatsEvaluator();
RecommenderBuilder recommenderBuilder = new RecommenderBuilder() {
public Recommender buildRecommender(DataModel model)
throws TasteException {
UserSimilarity similarity = new PearsonCorrelationSimilarity(
model);
UserNeighborhood neighborhood = new NearestNUserNeighborhood(2,
similarity, model);
return new GenericUserBasedRecommender(model, neighborhood,
similarity);
}
};
IRStatistics stats = evaluator.evaluate(recommenderBuilder, null,
model, null, 4, 4, 0.5);
System.out.println(stats.getPrecision());
System.out.println(stats.getRecall());
and the data in the file is:
1,101,5.0
1,102,3.0
1,103,2.5
2,101,2.0
2,102,2.5
2,103,5.0
2,104,2.0
3,101,2.5
3,104,4.0
3,105,4.5
3,107,5.0
4,101,5.0
4,103,3.0
4,104,4.5
4,106,4.0
5,101,4.0
5,102,3.0
5,103,2.0
5,104,4.0
5,105,3.5
5,106,4.0
When running the code above on the data file, I got the
java.lang.IllegalArgumentException: Illegal precision: NaN Why did this happen? I find something related here, but it is posted in 2009 and cannot explain my confusion.
Ultimately, the error means that no precision or recall could be computed, and this is because the test data set is so small that no meaningful tests were possible. I don't think it will be enough, but, change 0.5 to 1.0 and lower your threshold from 4 to 3.
The IllegalArgumentException is just a cosmetic bug that shouldn't occur. It was fixed in SVN a while ago. But it would just then show you that the precision and recall were undefined.