Interactions: get rid of Add() method for now, document the constructor
Interactions: add getter for interaction_list w/ default access
add CrossValidationSplit and SimpleSplit; make Interaction datatypes classes for more flexibility
add CrossValidationSplit and SimpleSplit; make Interaction datatypes classes for more flexibility
Wrap: exception handling in MeasureTime()
start to use splitting and new IO in ItemRecommendation (still throws exceptions)
add ByUserReaders
add ByItemReaders; avoid using indirect indexing (we use reference types anyway)
fix thinko in ByItemReaders
get rid of PosOnlyFeedbackCrossValidationSplit and PosOnlyFeedbackSimpleSplit