/// <summary>
/// Generates the negative ratings.
/// </summary>
/// <param name="itemHistogram">The item histogram.</param>
private void GenerateNegativeRatings(IDictionary <TItem, int> itemHistogram)
{
// Create the binary sum tree.
var items = itemHistogram.Keys.Select(key => key).ToList();
var histogramSampler = new HistogramSampler(
itemHistogram.Values.Select(value => Convert.ToInt32(Math.Pow(value, this.itemHistogramAdjustment))));
foreach (var userToRatedItems in this.ratedInstances)
{
var ratedItems = userToRatedItems.Value;
// In case the user has liked more than half of the items
int samplesCount = Math.Min(ratedItems.Count, items.Count - ratedItems.Count);
for (int i = 0; i < samplesCount; ++i)
{
// This is required not to run into an infinite loop.
for (int sampleAttempts = 0; sampleAttempts < SampleAttemptsCount; ++sampleAttempts)
{
var itemIndex = histogramSampler.Sample();
var ratedItem = new RatedItem(items[itemIndex], NegativeRatingValue);
if (!ratedItems.Contains(ratedItem))
{
histogramSampler.Take(itemIndex);
ratedItems.Add(ratedItem);
break;
}
}
}
}
}
public static RatedItem FromViewModel(RatedItemBaseViewModel vm)
{
var entity = new RatedItem();
FromViewModel(vm, entity);
return(entity);
}
public static RatedItemViewModel ToViewModel(RatedItem entity)
{
return(new RatedItemViewModel()
{
Id = entity.Id,
Name = entity.Name,
Rating = entity.Rating
});
}
/// <summary>
/// Generates the positive ratings and the item histogram.
/// </summary>
/// <param name="instanceSource">The source of positive instances.</param>
/// <param name="itemHistogram">The item histogram.</param>
/// <remarks>
/// The generation of these two entities is implemented in the same method for performance reasons.
/// By doing this, iteration over the positive observations is performed only once.
/// </remarks>
private void GeneratePositiveRatingsAndItemHistogram(
TInstanceSource instanceSource, out IDictionary <TItem, int> itemHistogram)
{
itemHistogram = new Dictionary <TItem, int>();
var instances = this.mapping.GetInstances(instanceSource);
foreach (TInstance instance in instances)
{
TUser user = this.mapping.GetUser(instanceSource, instance);
TItem item = this.mapping.GetItem(instanceSource, instance);
// Update the item histogram
if (!itemHistogram.ContainsKey(item))
{
itemHistogram.Add(item, 0);
}
++itemHistogram[item];
// Update the rated instances
HashSet <RatedItem> ratedItems;
if (!this.ratedInstances.TryGetValue(user, out ratedItems))
{
ratedItems = new HashSet <RatedItem>();
this.ratedInstances.Add(user, ratedItems);
}
var ratedItem = new RatedItem(item, PositiveRatingValue);
if (ratedItems.Contains(ratedItem))
{
throw new NotSupportedException(
string.Format(
"Multiple occurances of the same user-item pair are not supported. User: {0}, Item: {1}.",
user,
item));
}
ratedItems.Add(ratedItem);
}
}
protected bool Equals(RatedItem other)
{
return(string.Equals(Name, other.Name) && AvgRating.Equals(other.AvgRating) && Ratings == other.Ratings);
}
public static void FromViewModel(RatedItemBaseViewModel vm, RatedItem entity)
{
entity.Name = vm.Name;
entity.Rating = vm.Rating;
}