protected List <Rating> GetRecommendations(MyTable ratingTable, int N = 30)
{
List <Rating> recommendedItems = new List <Rating>();
ArrayList list = ratingTable.GetSubKeyList();
int[] mainKeys = new int[ratingTable.Keys.Count];
ratingTable.Keys.CopyTo(mainKeys, 0);
Parallel.ForEach(mainKeys, userId =>
{
Hashtable Nu = (Hashtable)ratingTable[userId]; // ratings of user u
List <Rating> predictedRatings = new List <Rating>();
foreach (int itemId in list)
{
if (!Nu.ContainsKey(itemId))
{
double p = Predict(userId, itemId, -1);
predictedRatings.Add(new Rating(userId, itemId, p));
}
}
List <Rating> sortedLi = predictedRatings.OrderByDescending(r => r.Score).ToList();
var selectedLi = sortedLi.GetRange(0, Math.Min(sortedLi.Count, N));
lock (recommendedItems)
{
recommendedItems.AddRange(selectedLi);
}
});
return(recommendedItems);
}
/// <summary>
/// Randomly sample negative ratings for each user from his/her rated ratings
/// </summary>
/// <param name="ratings">positive ratings</param>
/// <param name="ratio">ratio = #(negative samples) / #(positive samples)</param>
/// <param name="verbose"></param>
/// <returns></returns>
public static List <Rating> RandomSelectNegativeSamples(List <Rating> ratings, int ratio = 1, bool verbose = false)
{
if (verbose)
{
Console.WriteLine("ratio,{0}", ratio);
}
List <Rating> positiveRatings = new List <Rating>();
foreach (Rating r in ratings)
{
positiveRatings.Add(new Rating(r.UserId, r.ItemId, 1.0));
}
MyTable ratingTable = GetRatingTable(positiveRatings);
int[] items = (int[])ratingTable.GetSubKeyList().ToArray(typeof(int));
Random random = new Random();
foreach (int uId in ratingTable.Keys)
{
Hashtable subTable = (Hashtable)ratingTable[uId];
int counter = 0, ratedItems = subTable.Count;
while ((counter < ratedItems * ratio) && (counter < items.Length - ratedItems))
{
int iId = items[random.Next(items.Length)];
if (!subTable.ContainsKey(iId))
{
subTable.Add(iId, 0.0); // negative samples
counter++;
}
}
}
List <Rating> samples = new List <Rating>();
foreach (int uId in ratingTable.Keys)
{
Hashtable subTable = (Hashtable)ratingTable[uId];
foreach (int iId in subTable.Keys)
{
double score = (double)subTable[iId];
samples.Add(new Rating(uId, iId, score));
}
}
return(samples);
}
