HNSW update

Fix bugs

TestHNSW/HNSWDemo/Program.cs

@@ -77,13 +77,13 @@ namespace HNSWDemo
         static void Main(string[] args)
         {
             var dimensionality = 128;
-            var testCount = 1000;
-            var count = 100000;
-            var batchSize = 5000;
+            var testCount = 5000;
+            var count = 10000;
+            var batchSize = 1000;
             var samples = Person.GenerateRandom(dimensionality, count);
 
             var sw = new Stopwatch();
-            var world = new SmallWorld<float[]>(NSWOptions<float[]>.Create(6, 4, 120, 120, CosineDistance.ForUnits));
+            var world = new SmallWorld<float[]>(NSWOptions<float[]>.Create(6, 10, 200, 200, CosineDistance.ForUnits, false, false, selectionHeuristic: NeighbourSelectionHeuristic.SelectHeuristic));
 
             for (int i = 0; i < (count / batchSize); i++)
             {

ZeroLevel.HNSW/Layer.cs

@@ -94,7 +94,9 @@ namespace ZeroLevel.HNSW
             // W ← ep // dynamic list of found nearest neighbors
             W.Add(entryPointId, C[entryPointId]);
 
-
+            var popCandidate = new Func<(int, float)>(() => { var pair = C.OrderBy(e => e.Value).First(); C.Remove(pair.Key); return (pair.Key, pair.Value); });
+            var fartherFromResult = new Func<(int, float)>(() => { var pair = W.OrderByDescending(e => e.Value).First(); return (pair.Key, pair.Value); });
+            var fartherPopFromResult = new Action(() => { var pair = W.OrderByDescending(e => e.Value).First(); W.Remove(pair.Key); });
             // run bfs
             while (C.Count > 0)
             {
@@ -164,14 +166,14 @@ namespace ZeroLevel.HNSW
         /// <param name="extendCandidates">flag indicating whether or not to extend candidate list</param>
         /// <param name="keepPrunedConnections">flag indicating whether or not to add discarded elements</param>
         /// <returns>Output: M elements selected by the heuristic</returns>
-        public IDictionary<int, float> SELECT_NEIGHBORS_HEURISTIC(Func<int, float> distance, IDictionary<int, float> candidates, int M, bool extendCandidates, bool keepPrunedConnections)
+        public IDictionary<int, float> SELECT_NEIGHBORS_HEURISTIC(Func<int, float> distance, IDictionary<int, float> candidates, int M)
         {
             // R ← ∅
             var R = new Dictionary<int, float>();
             // W ← C // working queue for the candidates
             var W = new Dictionary<int, float>(candidates);
             // if extendCandidates // extend candidates by their neighbors
-            if (extendCandidates)
+            if (_options.ExpandBestSelection)
             {
                 var extendBuffer = new HashSet<int>();
                 // for each e ∈ C
@@ -191,7 +193,7 @@ namespace ZeroLevel.HNSW
                 // W ← W ⋃ eadj
                 foreach (var id in extendBuffer)
                 {
-                    W.Add(id, distance(id));
+                    W[id] = distance(id);
                 }
             }
 
@@ -201,7 +203,7 @@ namespace ZeroLevel.HNSW
 
             var popCandidate = new Func<(int, float)>(() => { var pair = W.OrderBy(e => e.Value).First(); W.Remove(pair.Key); return (pair.Key, pair.Value); });
             var fartherFromResult = new Func<(int, float)>(() => { if (R.Count == 0) return (-1, 0f); var pair = R.OrderByDescending(e => e.Value).First(); return (pair.Key, pair.Value); });
-            var popNearestDiscarded = new Func<(int, float)>(() => { var pair = Wd.OrderBy(e => e.Value).First(); W.Remove(pair.Key); return (pair.Key, pair.Value); });
+            var popNearestDiscarded = new Func<(int, float)>(() => { var pair = Wd.OrderBy(e => e.Value).First(); Wd.Remove(pair.Key); return (pair.Key, pair.Value); });
 
 
             // while │W│ > 0 and │R│< M
@@ -218,21 +220,21 @@ namespace ZeroLevel.HNSW
                     // R ← R ⋃ e
                     R.Add(e, ed);
                 }
-                // else
+                else
                 {
                     // Wd ← Wd ⋃ e
                     Wd.Add(e, ed);
                 }
+            }
             // if keepPrunedConnections // add some of the discarded // connections from Wd
-                if (keepPrunedConnections)
+            if (_options.KeepPrunedConnections)
             {
                 // while │Wd│> 0 and │R│< M
                 while (Wd.Count > 0 && R.Count < M)
                 {
                     // R ← R ⋃ extract nearest element from Wd to q
                     var nearest = popNearestDiscarded();
-                        R.Add(nearest.Item1, nearest.Item2);
-                    }
+                    R[nearest.Item1] = nearest.Item2;
                 }
             }
             //  return R

ZeroLevel.HNSW/Model/NSWOptions.cs

@@ -2,10 +2,24 @@
 
 namespace ZeroLevel.HNSW
 {
-    public sealed class NSWOptions<TItem>
+    /// <summary>
+    /// Type of heuristic to select best neighbours for a node.
+    /// </summary>
+    public enum NeighbourSelectionHeuristic
     {
-        public const int FARTHEST_DIVIDER = 3;
+        /// <summary>
+        /// Marker for the Algorithm 3 (SELECT-NEIGHBORS-SIMPLE) from the article. Implemented in <see cref="Algorithms.Algorithm3{TItem, TDistance}"/>
+        /// </summary>
+        SelectSimple,
+
+        /// <summary>
+        /// Marker for the Algorithm 4 (SELECT-NEIGHBORS-HEURISTIC) from the article. Implemented in <see cref="Algorithms.Algorithm4{TItem, TDistance}"/>
+        /// </summary>
+        SelectHeuristic
+    }
 
+    public sealed class NSWOptions<TItem>
+    {
         /// <summary>
         /// Mox node connections on Layer
         /// </summary>
@@ -24,19 +38,42 @@ namespace ZeroLevel.HNSW
         /// </summary>
         public readonly Func<TItem, TItem, float> Distance;
 
+        public readonly bool ExpandBestSelection;
+
+        public readonly bool KeepPrunedConnections;
+
+        public readonly NeighbourSelectionHeuristic SelectionHeuristic;
+
         public readonly int LayersCount;
 
 
-        private NSWOptions(int layersCount, int m, int ef, int ef_construction, Func<TItem, TItem, float> distance)
+        private NSWOptions(int layersCount,
+            int m,
+            int ef,
+            int ef_construction,
+            Func<TItem, TItem, float> distance,
+            bool expandBestSelection,
+            bool keepPrunedConnections,
+            NeighbourSelectionHeuristic selectionHeuristic)
         {
             LayersCount = layersCount;
             M = m;
             EF = ef;
             EFConstruction = ef_construction;
             Distance = distance;
+            ExpandBestSelection = expandBestSelection;
+            KeepPrunedConnections = keepPrunedConnections;
+            SelectionHeuristic = selectionHeuristic;
         }
 
-        public static NSWOptions<TItem> Create(int layersCount, int M, int EF, int EF_construction, Func<TItem, TItem, float> distance) =>
-            new NSWOptions<TItem>(layersCount, M, EF, EF_construction, distance);
+        public static NSWOptions<TItem> Create(int layersCount,
+            int M,
+            int EF,
+            int EF_construction,
+            Func<TItem, TItem, float> distance,
+            bool expandBestSelection = false,
+            bool keepPrunedConnections = false,
+            NeighbourSelectionHeuristic selectionHeuristic = NeighbourSelectionHeuristic.SelectSimple) =>
+            new NSWOptions<TItem>(layersCount, M, EF, EF_construction, distance, expandBestSelection, keepPrunedConnections, selectionHeuristic);
     }
 }

ZeroLevel.HNSW/Services/CompactBiDirectionalLinksSet.cs

@@ -14,15 +14,14 @@ namespace ZeroLevel.HNSW
 
         private SortedList<long, float> _set = new SortedList<long, float>();
 
-        public (int, int, float) this[int index]
+        public (int, int) this[int index]
         {
             get
             {
                 var k = _set.Keys[index];
-                var d = _set.Values[index];
                 var id1 = (int)(k >> HALF_LONG_BITS);
                 var id2 = (int)(k - (((long)id1) << HALF_LONG_BITS));
-                return (id1, id2, d);
+                return (id1, id2);
             }
         }
 
@@ -72,11 +71,23 @@ namespace ZeroLevel.HNSW
             {
                 _set.Remove(k_id1_id2);
                 _set.Remove(k_id2_id1);
+                if (!_set.ContainsKey(k_id_id1))
+                {
                     _set.Add(k_id_id1, distanceToId1);
+                }
+                if (!_set.ContainsKey(k_id1_id))
+                {
                     _set.Add(k_id1_id, distanceToId1);
+                }
+                if (!_set.ContainsKey(k_id_id2))
+                {
                     _set.Add(k_id_id2, distanceToId2);
+                }
+                if (!_set.ContainsKey(k_id2_id))
+                {
                     _set.Add(k_id2_id, distanceToId2);
                 }
+            }
             finally
             {
                 _rwLock.ExitWriteLock();

ZeroLevel.HNSW/SmallWorld.cs

@@ -192,7 +192,9 @@ namespace ZeroLevel.HNSW
 
         private IDictionary<int, float> SelectBestForConnecting(int layer, Func<int, float> distance, IDictionary<int, float> candidates)
         {
+            if(_options.SelectionHeuristic == NeighbourSelectionHeuristic.SelectSimple)
                 return _layers[layer].SELECT_NEIGHBORS_SIMPLE(distance, candidates, GetM(layer));
+            return _layers[layer].SELECT_NEIGHBORS_HEURISTIC(distance, candidates, GetM(layer));
         }
 
         /// <summary>