Added cosine similarity

Sources/SwiftNLP/1. Data Collection/HNSW/CosineSimilarityMetric.swift

+//
+//  CosineSimilarityMetric.swift
+//
+//
+//  Created by Mingchung Xia on 2024-03-14.
+//
+
+import Foundation
+import Accelerate
+import SimilarityMetric
+
+// MARK: May be improved on using Surge/Nifty
+// See https://developer.apple.com/documentation/accelerate/vdsp-snv
+
+public struct CosineSimilarityMetric<Vector: Collection & Codable>: SimilarityMetric where Vector.Element: BinaryFloatingPoint {
+    public func similarity(between someItem: Vector, _ otherItem: Vector) -> Vector.Element {
+        /// Convert vectors to Double for Accelerate functions
+        let someItemDoubles = someItem.map { Double($0) }
+        let otherItemDoubles = otherItem.map { Double($0) }
+        
+        /// Calculate dot product
+        var dotProduct: Double = 0.0
+        vDSP_dotprD(someItemDoubles, 1, otherItemDoubles, 1, &dotProduct, vDSP_Length(someItemDoubles.count))
+        
+        /// Calculate magnitude of vectors
+        var someItemMagnitudeSquared: Double = 0.0
+        var otherItemMagnitudeSquared: Double = 0.0
+        vDSP_svesqD(someItemDoubles, 1, &someItemMagnitudeSquared, vDSP_Length(someItemDoubles.count))
+        vDSP_svesqD(otherItemDoubles, 1, &otherItemMagnitudeSquared, vDSP_Length(otherItemDoubles.count))
+        let someItemMagnitude = sqrt(someItemMagnitudeSquared)
+        let otherItemMagnitude = sqrt(otherItemMagnitudeSquared)
+        
+        /// Calculate the cosine similarity
+        let cosineSimilarity = dotProduct / (someItemMagnitude * otherItemMagnitude)
+        
+        /// Convert back to type Vector.Element
+        return Vector.Element(cosineSimilarity)
+    }
+}

Sources/SwiftNLP/1. Data Collection/HNSW/DeterministicDurableVectorIndex.swift

@@ -41,7 +41,8 @@ extension DurableVectorIndex {
 
 public struct DeterministicDurableVectorIndex/*<Vector: Collection & Codable> where Vector.Element: BinaryFloatingPoint*/ {
     public typealias Vector = [Double]
-    public typealias Index = DurableVectorIndex<CartesianDistanceMetric<Vector>, Vector.Element>
+//    public typealias Index = DurableVectorIndex<CartesianDistanceMetric<Vector>, Vector.Element>
+    public typealias Index = DurableVectorIndex<CosineSimilarityMetric<Vector>, Vector.Element>
     public var base: Index
     public var typicalNeighborhoodSize: Int
     public var size: Int = 0
@@ -50,7 +51,8 @@ public struct DeterministicDurableVectorIndex/*<Vector: Collection & Codable> wh
     // private var drng = DeterministicRandomNumberGenerator(seed: 1)
     
     public init(namespace: String, typicalNeighborhoodSize: Int = 20, in transaction: Transaction) throws {
-        let metric = CartesianDistanceMetric<Vector>()
+//        let metric = CartesianDistanceMetric<Vector>()
+        let metric = CosineSimilarityMetric<Vector>()
         let config = Config.unstableDefault(typicalNeighborhoodSize: typicalNeighborhoodSize)
         self.base = try Index(
             namespace: namespace,

Tests/SwiftNLPTests/2. Encoding/HNSWTests.swift

@@ -283,17 +283,17 @@ final class HNSWTests: XCTestCase {
         let transaction = try Transaction.begin(.write, in: env)
         
         /// Saving the memory map to disk
-//        var corpus = try DurableHNSWCorpus(
-//            encoder: _documentEncoder,
-//            namespace: "testbasicqueryexampledurable",
-//            in: transaction
-//        )
-//        
-//        for doc in docs {
-//            try corpus.addUntokenizedDocument(doc, in: transaction)
-//        }
-//        
-//        corpus.saveDictionaryToDownloads(fileName: "dictionary.mmap")
+        var corpus = try DurableHNSWCorpus(
+            encoder: _documentEncoder,
+            namespace: "testbasicqueryexampledurable",
+            in: transaction
+        )
+        
+        for doc in docs {
+            try corpus.addUntokenizedDocument(doc, in: transaction)
+        }
+        
+        corpus.saveDictionaryToDownloads(fileName: "dictionary.mmap")
         
         try transaction.commit()