/// <p>
/// Like {@link #GenericItemSimilarity(ItemSimilarity, DataModel)} )}, but will only keep the specified
/// number of similarities from the given {@link DataModel}. It will keep those with the highest similarity
/// -- those that are therefore most important.
/// </p>
///
/// <p>
/// Thanks to tsmorton for suggesting this and providing part of the implementation.
/// </p>
///
/// @param otherSimilarity
/// other {@link ItemSimilarity} to get similarities from
/// @param dataModel
/// data model to get items from
/// @param maxToKeep
/// maximum number of similarities to keep
/// @throws TasteException
/// if an error occurs while accessing the {@link DataModel} items
public GenericItemSimilarity(IItemSimilarity otherSimilarity,
IDataModel dataModel,
int maxToKeep)
{
long[] itemIDs = GenericUserSimilarity.longIteratorToList(dataModel.GetItemIDs());
var it = new DataModelSimilaritiesIterator(otherSimilarity, itemIDs);
var keptSimilarities = TopItems.GetTopItemItemSimilarities(maxToKeep, it);
initSimilarityMaps(keptSimilarities.GetEnumerator());
}
/// <p>
/// Builds a list of item-item similarities given an {@link ItemSimilarity} implementation and a
/// {@link DataModel}, rather than a list of {@link ItemItemSimilarity}s.
/// </p>
///
/// <p>
/// It's valid to build a {@link GenericItemSimilarity} this way, but perhaps missing some of the point of an
/// item-based recommender. Item-based recommenders use the assumption that item-item similarities are
/// relatively fixed, and might be known already independent of user preferences. Hence it is useful to
/// inject that information, using {@link #GenericItemSimilarity(Iterable)}.
/// </p>
///
/// @param otherSimilarity
/// other {@link ItemSimilarity} to get similarities from
/// @param dataModel
/// data model to get items from
/// @throws TasteException
/// if an error occurs while accessing the {@link DataModel} items
public GenericItemSimilarity(IItemSimilarity otherSimilarity, IDataModel dataModel)
{
long[] itemIDs = GenericUserSimilarity.longIteratorToList(dataModel.GetItemIDs());
initSimilarityMaps(new DataModelSimilaritiesIterator(otherSimilarity, itemIDs));
}