[GitHub] [ignite] avplatonov commented on a change in pull request #6849: IGNITE-12148: [ML] Recommendation Engine

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avplatonov commented on a change in pull request #6849: IGNITE-12148: [ML] Recommendation Engine
URL: https://github.com/apache/ignite/pull/6849#discussion_r322625278
 
 

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 File path: examples/src/main/java/org/apache/ignite/examples/ml/recommendation/MovieLensExample.java
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.ignite.examples.ml.recommendation;
+
+import java.io.IOException;
+import javax.cache.Cache;
+import org.apache.ignite.Ignite;
+import org.apache.ignite.IgniteCache;
+import org.apache.ignite.Ignition;
+import org.apache.ignite.cache.affinity.rendezvous.RendezvousAffinityFunction;
+import org.apache.ignite.cache.query.QueryCursor;
+import org.apache.ignite.cache.query.ScanQuery;
+import org.apache.ignite.configuration.CacheConfiguration;
+import org.apache.ignite.ml.dataset.impl.cache.CacheBasedDatasetBuilder;
+import org.apache.ignite.ml.environment.LearningEnvironmentBuilder;
+import org.apache.ignite.ml.recommendation.ObjectSubjectRatingTriplet;
+import org.apache.ignite.ml.recommendation.RecommendationModel;
+import org.apache.ignite.ml.recommendation.RecommendationTrainer;
+import org.apache.ignite.ml.util.MLSandboxDatasets;
+import org.apache.ignite.ml.util.SandboxMLCache;
+
+/**
+ * Example of recommendation system based on MovieLens dataset (see https://grouplens.org/datasets/movielens/).
+ * In this example we create a cache with MovieLens rating data. Each entry in this cache represnts a rating point
+ * (raiting set by a single user to a single movie). Then we pass this cache to {@link RecommendationTrainer} and so
+ * that train {@link RecommendationModel}. This model predices rating with assumed to be set by any user to any movie.
+ * When model is ready we calculate R2 score.
+ */
+public class MovieLensExample {
+    /** Run example. */
+    public static void main(String[] args) throws IOException {
+        System.out.println();
+        System.out.println(">>> Recommendation system over cache based dataset usage example started.");
+        // Start ignite grid.
+        try (Ignite ignite = Ignition.start("examples/config/example-ignite.xml")) {
+            System.out.println(">>> Ignite grid started.");
+
+            IgniteCache<Integer, RatingPoint> movielensCache = loadMovieLensDataset(ignite, 10_000);
+            try {
+                LearningEnvironmentBuilder envBuilder = LearningEnvironmentBuilder.defaultBuilder().withRNGSeed(1);
+                RecommendationTrainer trainer = new RecommendationTrainer()
+                    .withMaxIterations(-1)
+                    .withMinMdlImprovement(10)
+                    .withBatchSize(10)
+                    .withLearningRate(10)
+                    .withLearningEnvironmentBuilder(envBuilder)
+                    .withTrainerEnvironment(envBuilder.buildForTrainer());
+
+                RecommendationModel<Integer, Integer> mdl = trainer.fit(
+                    new CacheBasedDatasetBuilder<>(ignite, movielensCache)
+                );
+
+                double mean = 0;
+                try (QueryCursor<Cache.Entry<Integer, RatingPoint>> cursor = movielensCache.query(new ScanQuery<>())) {
 
 Review comment:
   We can compute RSS using just one query, there is no need to do two-pass process of estimation. Please, have a look at this page: https://en.wikipedia.org/wiki/Variance . Variance could be computed using two means - mean value of original data and mean value of squared data. We can compute these two values to determine variance that used in RSS formula.

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