/// <summary>
/// Initializes a new instance of the
/// <see cref="RecommenderEvaluator{TInstanceSource, TUser, TItem, TGroundTruthRating, TPredictedRating, TPredictedRatingDist}"/> class.
/// </summary>
/// <param name="mapping">The mapping used for accessing data.</param>
/// <exception cref="ArgumentNullException">Thrown if the given mapping is null.</exception>
public RecommenderEvaluator(IRecommenderEvaluatorMapping <TInstanceSource, TUser, TItem, TGroundTruthRating> mapping)
{
if (mapping == null)
{
throw new ArgumentNullException("mapping");
}
this.mapping = mapping;
}
/// <summary>
/// Finds all the items which have been rated by the same user as <paramref name="queryItem"/>.
/// </summary>
/// <typeparam name="TInstanceSource">The type of a source of instances.</typeparam>
/// <typeparam name="TUser">The type of a user.</typeparam>
/// <typeparam name="TItem">The type of an item.</typeparam>
/// <typeparam name="TRating">The type of a rating.</typeparam>
/// <param name="mapping">The mapping.</param>
/// <param name="instanceSource">The instance source with items.</param>
/// <param name="queryItem">The query item.</param>
/// <returns>
/// A dictionary which maps items from the <paramref name="instanceSource"/> to the lists of users
/// who has rated both the item and <paramref name="queryItem"/>. Only items with at least one such user are returned.
/// </returns>
public static Dictionary <TItem, List <TUser> > GetItemsRatedBySameUsers <TInstanceSource, TUser, TItem, TRating>(
this IRecommenderEvaluatorMapping <TInstanceSource, TUser, TItem, TRating> mapping,
TInstanceSource instanceSource,
TItem queryItem)
{
if (mapping == null)
{
throw new ArgumentNullException("mapping");
}
return(GetEntitiesWithCommonRatedEntities(
queryItem,
i => mapping.GetUsersWhoRatedItem(instanceSource, i),
u => mapping.GetItemsRatedByUser(instanceSource, u)));
}
