/// <summary>
/// Initialize Multiset from HashSet, each ID has multiplicity 1
/// </summary>
/// <param name="friends"></param>
/// <returns></returns>
public static IDMultiset Create(HashSet<SubscriberID> friends)
{
var multiset = new IDMultiset();
foreach (SubscriberID friend in friends)
{
multiset[friend] = 1;
}
return multiset;
}
/// <summary>
/// Initialize Multiset from HashSet, each ID has multiplicity 1
/// </summary>
/// <param name="friends"></param>
/// <returns></returns>
public static IDMultiset Create(HashSet <SubscriberID> friends)
{
var multiset = new IDMultiset();
foreach (SubscriberID friend in friends)
{
multiset[friend] = 1;
}
return(multiset);
}
public IDMultisetItemList PotentialFriendsParallel(SubscriberID id, int maxCandidates)
{
object locker = new object();
IDMultiset candidates = new IDMultiset();
Parallel.ForEach(subscribers[id].Friends, // Map over friends
() => Multiset.Create(new HashSet <SubscriberID>()), // init thread-local state localFoafs with empty Multiset
(friend, loopState, localFoafs) =>
{
var foafs = subscribers[friend].FriendsCopy();
foafs.RemoveWhere(foaf => foaf == id || subscribers[id].Friends.Contains(foaf)); // remove self, own friends
return(Multiset.Union(localFoafs, Multiset.Create(foafs))); // Reduce, thread-local
},
localFoafs => { lock (locker) candidates = Multiset.Union(localFoafs, candidates); }); // Reduce, among threads
return(Multiset.MostNumerous(candidates, maxCandidates)); // postprocess results of Reduce
}
/// <summary>
/// Multiset union.
/// </summary>
/// <param name="multiset1">First Multiset</param>
/// <param name="multiset2">Second Multiset</param>
/// <returns>Union of Multiset1 and Multiset2</returns>
public static IDMultiset Union(IDMultiset multiset1, IDMultiset multiset2)
{
if (multiset1.Count < multiset2.Count)
{
return Union(multiset2, multiset1);
}
else
{
var union = new IDMultiset();
foreach (var item in multiset1)
{
union.Add(item.Key, item.Value);
}
foreach (var item in multiset2)
{
var friend = item.Key;
var count = item.Value;
union[friend] = union.ContainsKey(friend) ? union[friend] + count : count;
}
return union;
}
}
/// <summary>
/// Multiset union.
/// </summary>
/// <param name="multiset1">First Multiset</param>
/// <param name="multiset2">Second Multiset</param>
/// <returns>Union of Multiset1 and Multiset2</returns>
public static IDMultiset Union(IDMultiset multiset1, IDMultiset multiset2)
{
if (multiset1.Count < multiset2.Count)
{
return(Union(multiset2, multiset1));
}
else
{
var union = new IDMultiset();
foreach (var item in multiset1)
{
union.Add(item.Key, item.Value);
}
foreach (var item in multiset2)
{
var friend = item.Key;
var count = item.Value;
union[friend] = union.ContainsKey(friend) ? union[friend] + count : count;
}
return(union);
}
}
public IDMultisetItemList PotentialFriendsSequential(SubscriberID id, int maxCandidates)
{
// Map
var foafsList = new List <IDMultiset>();
foreach (SubscriberID friend in subscribers[id].Friends)
{
var foafs = subscribers[friend].FriendsCopy();
foafs.RemoveWhere(foaf => foaf == id || subscribers[id].Friends.Contains(foaf)); // remove self, own friends
foafsList.Add(Multiset.Create(foafs));
}
// Reduce
IDMultiset candidates = new IDMultiset();
foreach (IDMultiset foafs in foafsList)
{
candidates = Multiset.Union(foafs, candidates);
}
// Postprocess
return(Multiset.MostNumerous(candidates, maxCandidates));
}
public IDMultisetItemList PotentialFriendsSequential(SubscriberID id, int maxCandidates)
{
// Map
var foafsList = new List<IDMultiset>();
foreach (SubscriberID friend in subscribers[id].Friends)
{
var foafs = subscribers[friend].FriendsCopy();
foafs.RemoveWhere(foaf => foaf == id|| subscribers[id].Friends.Contains(foaf)); // remove self, own friends
foafsList.Add(Multiset.Create(foafs));
}
// Reduce
IDMultiset candidates = new IDMultiset();
foreach (IDMultiset foafs in foafsList)
{
candidates = Multiset.Union(foafs, candidates);
}
// Postprocess
return Multiset.MostNumerous(candidates, maxCandidates);
}
public IDMultisetItemList PotentialFriendsParallel(SubscriberID id, int maxCandidates)
{
object locker = new object();
IDMultiset candidates = new IDMultiset();
Parallel.ForEach(subscribers[id].Friends, // Map over friends
() => Multiset.Create(new HashSet<SubscriberID>()), // init thread-local state localFoafs with empty Multiset
(friend, loopState, localFoafs) =>
{
var foafs = subscribers[friend].FriendsCopy();
foafs.RemoveWhere(foaf => foaf == id || subscribers[id].Friends.Contains(foaf)); // remove self, own friends
return Multiset.Union(localFoafs, Multiset.Create(foafs)); // Reduce, thread-local
},
localFoafs => { lock (locker) candidates = Multiset.Union(localFoafs, candidates); }); // Reduce, among threads
return Multiset.MostNumerous(candidates, maxCandidates); // postprocess results of Reduce
}