From 2b79fcc0414dd382d1467286d2030f4cd15b3460 Mon Sep 17 00:00:00 2001
From: Michael Zhang <mail@mzhang.io>
Date: Tue, 7 Sep 2021 10:38:32 -0500
Subject: [PATCH] not working yet

---
 .../AssociationItemBasedItemRecommender.java  | 26 +++++++++++++++++++
 .../assoc/BasicAssociationModelProvider.java  |  6 ++++-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/nonpers-assignment/src/main/java/org/lenskit/mooc/nonpers/assoc/AssociationItemBasedItemRecommender.java b/nonpers-assignment/src/main/java/org/lenskit/mooc/nonpers/assoc/AssociationItemBasedItemRecommender.java
index 4cb4452..e545bd2 100644
--- a/nonpers-assignment/src/main/java/org/lenskit/mooc/nonpers/assoc/AssociationItemBasedItemRecommender.java
+++ b/nonpers-assignment/src/main/java/org/lenskit/mooc/nonpers/assoc/AssociationItemBasedItemRecommender.java
@@ -5,6 +5,7 @@ import org.lenskit.api.Result;
 import org.lenskit.api.ResultList;
 import org.lenskit.basic.AbstractItemBasedItemRecommender;
 import org.lenskit.results.Results;
+import org.lenskit.results.BasicResult;
 import org.lenskit.util.collections.LongUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -14,6 +15,8 @@ import javax.inject.Inject;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Set;
+import java.util.PriorityQueue;
+import java.util.AbstractMap;
 
 /**
  * An item-based item scorer that uses association rules.
@@ -65,8 +68,31 @@ public class AssociationItemBasedItemRecommender extends AbstractItemBasedItemRe
      */
     private ResultList recommendItems(int n, long refItem, LongSet candidates) {
         List<Result> results = new ArrayList<>();
+        
+        class Score implements Comparable<Score> {
+            private double score;
+            private long id;
+            public Score(double score, long id) { this.score = score; this.id = id; }
+
+            @Override
+            public int compareTo(Score other) {
+                return new Double(-this.score).compareTo(new Double(-other.score));
+            }
+        }
 
         // TODO Compute the n highest-scoring items from candidates
+        PriorityQueue<Score> scoring = new PriorityQueue();
+        for (long cand : candidates) {
+            double score = model.getItemAssociation(refItem, cand);
+            scoring.offer(new Score(score, cand));
+        }
+
+        for (int i = 0; i < n; ++i) {
+            Score entry = scoring.poll();
+            if (entry == null) break;
+
+            results.add(new BasicResult(entry.id, entry.score));
+        }
 
         return Results.newResultList(results);
     }
diff --git a/nonpers-assignment/src/main/java/org/lenskit/mooc/nonpers/assoc/BasicAssociationModelProvider.java b/nonpers-assignment/src/main/java/org/lenskit/mooc/nonpers/assoc/BasicAssociationModelProvider.java
index db8d722..415941b 100644
--- a/nonpers-assignment/src/main/java/org/lenskit/mooc/nonpers/assoc/BasicAssociationModelProvider.java
+++ b/nonpers-assignment/src/main/java/org/lenskit/mooc/nonpers/assoc/BasicAssociationModelProvider.java
@@ -12,6 +12,7 @@ import org.lenskit.util.io.ObjectStream;
 import javax.inject.Inject;
 import javax.inject.Provider;
 import java.util.List;
+import java.util.HashSet;
 
 /**
  * Build a model for basic association rules.  This class computes the association for all pairs of items.
@@ -71,7 +72,10 @@ public class BasicAssociationModelProvider implements Provider<AssociationModel>
                 LongSortedSet yUsers = yEntry.getValue();
 
                 // TODO Compute P(Y & X) / P(X) and store in itemScores
-                itemScores.addTo(yId, 1.0 / xUsers.size());
+                HashSet ySet = new HashSet(yUsers), xSet = new HashSet(xUsers);
+                ySet.retainAll(xSet);
+                double p = ySet.size() / xSet.size();
+                itemScores.put(yId, p);
             }
 
             // save the score map to the main map