brief contents

1 · Meet Apache Mahout 1

PART 1 RECOMMENDATIONS

11

2 · Introducing recommenders 13 3 · Representing recommender data 26 4 · Making recommendations 41 5 · Taking recommenders to production 70 6 · Distributing recommendation computations 91

PART 2 CLUSTERING

115

7 · Introduction to clustering 117 8 · Representing data 130 9 · Clustering algorithms in Mahout 145 10 · Evaluating and improving clustering quality 184 11 · Taking clustering to production 198 12 · Real-world applications of clustering 210

VI

BRIEF CONTENTS

PART 3 CLASSIFICATION

225

13 · Introduction to classification 227 14 · Training a classifier 255 15 · Evaluating and tuning a classifier 281 16 · Deploying a classifier 307 17 · case study: Shop It To Me 341

contents

preface xvii acknowledgments xix about this book xx about multimedia extras xxiii about the cover illustration xxv 1 Meet Apache Mahout 1 -*- 1.1 Mahout's story 2 1.2 Mahout's machine learning themes 3 Recommender engines 3 * Clustering 3 · Classification 4 1.3 Tackling large scale with Mahout and Hadoop 5 1.4 Setting up Mahout 6 Java and IDEs 7 · Installing Maven 8 · Installing Mahout 8 · Installing Hadoop 9 1.5 Summary 9

PART 1 RECOMMENDATIONS

11

Introducing recommenders 13 2.1 Defining recommendation 14

CONTENTS 2.2 Running a first recommender engine 15 Creating the input 15 * Creating a recommender 16 Analyzing the output 17 2.3 Evaluating a recommender 18 Training data and scoring 18* Running RecommenderEvaluator 19 * Assessing the result 20 2.4 Evaluating precision and recall 21 Running RecommenderlRStatsEvaluator 21 * Problems with precision and recall 23 2.5 Evaluating the GroupLens data set 23 Extracting the recommender input 23 * Experimenting with other recommenders 24 2.6 Summary 25 Representing recommender data 26 3.1 Representing preference data 27 The Preference object 27* PreferenceArray and implementations 28 * Speeding up collections 28 FastBylDMap and FastlDSet 29 3.2 In-memory DataModels 30 GenericDataModel 30 * File-based data 30 * Refreshable components 31 * Update files 32 * Database-based data 32 JDBC and MySQL 32 * Configuring via JNDI 33 Configuring programmatically 34 3.3 Coping without preference values 34 When to ignore values 35 * In-memory representations without preference values 36* Selecting compatible implementations 37 3.4 Summary 39 Making recommendations 41 4.1 Understanding user-based recommendation 42 When recommendation goes wrong 42 * When recommendation goes right 42 4.2 Exploring the user-based recommender 43 The algorithm 43 * Implementing the algorithm with GenericUserBasedRecommender 44 * Exploring with GroupLens 45 * Exploring user neighborhoods 46 Fixed-size neighborhoods 46* Threshold-based neighborhood 47

CONTENTS 4.3 Exploring similarity metrics 48 Pearson Correlation-based similarity 48 * Pearson correlation problems 50 * Employing weighting 50 * Defining similarity by Euclidean distance 51 * Adapting the cosine measure similarity 52 * Defining similarity by relative rank with the Spearman correlation 52 * Ignoring preference values in similarity with the Tanimoto coefficient 54 * Computing smarter similarity with a log-likelihood test 55 * Inferring preferences 56 4.4 Item-based recommendation 56 The algorithm 57 * Exploring the item-based recommender 58 4.5 Slope-one recommender 59 The algorithm 60 * Slope-one in practice 61 * DiffStorage and memory considerations 62 * Distributing the precomputation 62 4.6 New and experimental recommenders 63 Singular value decomposition--based recommenders 63 Linear interpolation item--based recommendation 64 Cluster-based recommendation 65 4.7 Comparison to other recommenders 66 Injecting content-based techniques into Mahout 66 Looking deeper into content-based recommendation 67 Comparison to model-based recommenders 67 4.8 Summary 68 5 Taking recommenders to production 70 5.1 Analyzing example data from a dating site 71 5.2 Finding an effective recommender 72 User-based recommenders 73 * Item-based recommenders 74 Slope-one recommender 75 * Evaluating precision and recall 75 Evaluating Performance 76 5.3 Injecting domain-specific information 77 Employing a custom item similarity metric 77 * Recommending based on content 78 * Modifying recommendations with IDRescorer 79 * Incorporating gender in an IDRescorer 80 Packaging a custom recommender 82 5.4 Recommending to anonymous users 83 Temporary users with PlusAnonymousUserDataModel 84 Aggregating anonymous users 85 5.5 Creating a web-enabled recommender 86 Packaging a WAR file 86* Testing deployment 87

CONTENTS 5.6 Updating and monitoring the recommender 88 5.7 Summary 89 Distributing recommendation computations 91 6.1 Analyzing the Wikipedia data set 92 Struggling with scale 93 * Evaluating benefits and drawbacks of distributing computations 93 6.2 Designing a distributed item-based algorithm 95 Constructing a co-occurrence matrix 95 * Computing user vectors 96 · Producing the recommendations 96 Understanding the results 97 * Towards a distributed implementation 98 6.3 Implementing a distributed algorithm with MapReduce 98 Introducing MapReduce 98 * Translating to MapReduce: generating user vectors 99 * Translating to MapReduce: calculating co-occurrence 100* Translating to MapReduce: rethinking matrix multiplication 101 * Translating to MapReduce: matrix multiplication by partial products 102 Translating to MapReduce: making recommendations 105 6.4 Running MapReduces with Hadoop 107 Setting up Hadoop 107* Running recommendations with Hadoop 108* Configuring mappers and reducers 110 6.5 Pseudo-distributing a recommender 110 6.6 Looking beyond first steps with recommendations 112 Running in the cloud 112 * Imagining unconventional uses of recommendations 113 6.7 Summary 114

PART 2 CLUSTERING

115

7 Introduction to clustering 117 7.1 Clustering basics 118 7.2 Measuring the similarity of items 119 7.3 Hello World: running a simple clustering example 120 Creating the input 120* Using Mahout clustering 122 Analyzing the output 125

CONTENTS 7.4 Exploring distance measures 125 Euclidean distance measure 126 * Squared Euclidean distance measure 126 * Manhattan distance measure 126 * Cosine distance measure 127* Tanimoto distance measure 128 Weighted distance measure 128 7.5 Hello World again! Trying out various distance measures 129 7.6 Summary 129 Representing data 130 8.1 Visualizing vectors 131 Transforming data into vectors 132 * Preparing vectors for use by Mahout 134 8.2 Representing text documents as vectors 135 Improving weighting with TF-IDF 136 * Accounting for word dependencies with n-gram collocations 137 8.3 Generating vectors from documents 138 8.4 Improving quality of vectors using normalization 143 8.5 Summary 144 Clustering algorithms in Mahout 145 9.1 K-means clustering 146 All you need to know about k-means 147 * Running k-means clustering 148 * Finding the perfect k using canopy clustering 155 * Case study: clustering news articles using k-means 160 9.2 Beyond k-means: an overview of clustering techniques 163 Different kinds of clustering problems 163 * Different clustering approaches 166 9.3 Fuzzy k-means clustering 168 Running fuzzy k-means clustering 168 * How fuzzy is too fuzzy ? 170 * Case study: clustering news articles using fuzzy k-means 170 9.4 Model-based clustering 171 Deficiencies of k-means 172 * Dirichlet clustering 173 Running a model-based clustering example 174

CONTENTS 9.5 Topic modeling using latent Dirichlet allocation (LDA) 177 Understanding latent Dirichlet analysis 178 * TF-IDF vs. LDA 179 * Tuning the parameters of LDA 179 * Case study: finding topics in news documents 180 * Applications of topic modeling 182 9.6 Summary 182 Evaluating and improving clustering quality 184 10.1 Inspecting clustering output 185 10.2 Analyzing clustering output 187 Distance measure and feature selection 188* Inter-cluster and intra-cluster distances 188 * Mixed and overlapping clusters 191 10.3 Improving clustering quality 192 Improving document vector generation 192* Writing a custom distance measure 195 10.4 Summary 197 11 Taking clustering to production 198 11.1 Quick-start tutorial for running clustering on Hadoop 199 Running clustering on a local Hadoop cluster 199 Customizing Hadoop configurations 201 11.2 Tuning clustering performance 202 Avoiding performance pitfalls in CPU-bound operations 203 Avoiding performance pitfalls in I/O-bound operations 204 11.3 Batch and online clustering 205 Case study: online news clustering 206 * Case study: clustering Wikipedia articles 207 11.4 Summary 209 12 Real-world applications of clustering 210 12.1 Finding similar users on Twitter 211 Data preprocessing and feature weighting 211 * Avoiding common pitfalls in feature selection 212 12.2 Suggesting tags for artists on Lastim 216 Tag suggestion using co-occurrence 216* Creating a dictionary of Last.fm artists 217 * Converting Last.fm tags into Vectors with musicians as features 219* Running k-means over the Last.fm data 220

CONTENTS

X1U

12.3 Analyzing the Stack Overflow data set 221 Parsing the Stack Overflow data set 222 * Finding clustering problems in Stack Overflow 222 12 A Summary 224

PART 3 CLASSIFICATION

225

13 Introduction to classification 227 13.1 Why use Mahout for classification? 228 13.2 The fundamentals of classification systemS 229 Differences between classification, recommendation, and clustering 230 * Applications of classification 231 13.3 How classification works 232 Models 234 * Training versus test versus production 234 predictor variables versus target variable 234 * Records, fields, and values 235' The four types of values for predictor variables 236 * Supervised versus unsupervised learning 238 13.4 Work flow in a typical classification project 239 Workflow for stage 1: training the classification model 240 Workflow for stage 2: evaluating the classification model 245 Workflow for stage 3: using the model in production 245 13.5 Step-by-step simple classification example 245 The data and the challenge 246 * Training a model to find colorfill: preliminary thinking 246 « Choosing a learning algorithm to train the model 247 * Improving performance of the color-fill classifier 250 13.6 Summary 254 14 Training a classifier 255 14.1 Extracting features to build a Mahout classifier 256 14.2 Preprocessing raw data into classifiable data 257 Transforming raw data 258 * Computational marketing example 258 14.3 Converting classifiable data into vectors 260 Representing data as a vector 260 * Feature hashing with Mahout APIs 261

CONTENTS 14.4 Classifying the 20 newsgroups data set with SGD 265 Getting started: previewing the data set 266 * Parsing and tokenizing features for the 20 newsgroups data 268 Training code for the 20 newsgroups data 268 14.5 Choosing an algorithm to train the classifier 273 Nonparallel but powerful: using SGD and SVM 274* The power of the naive classifier: using naive Bayes and complementary naive Bayes 275* Strength in elaborate structure: using Random Forests 276 14.6 Classifying the 20 newsgroups data with naive Bayes 276 Getting started: data extraction for naive Bayes 276* Training the naive Bayes classifier 278 * Testing a naive Bayes model 278 14.7 Summary 280 15 Evaluating and tuning a classifier 281 15.1 Classifier evaluation in Mahout 282 Getting rapid feedback 282 * Deciding what "good" means 282 Recognizing the difference in cost of errors 284 15.2 The classifier evaluation API 284 Computation ofAUC 285 * Confusion matrices and entropy matrices 287* Computing average log likelihood 289 Dissecting a model 290* Performance of the SGD classifier with 20 newsgroups 291 15.3 When classifiers go bad 295 Target leaks 295 * Broken Feature Extraction 298 15.4 Tuning for better performance 300 Tuning the problem 300 * Tuning the classifier 304 15.5 Summary 306 16 Deploying a classifier 307 16.1 Process for deployment in huge systems 308 Scope out the problem 308 * Optimize feature extraction as needed 309 * Optimize vector encoding as needed 309 Deploy a scalable classifier service 310 16.2 Determining scale and speed requirements 310 How big is big? 310* Balancing big versus fast 312

CONTENTS

XV

16.3 Building a training pipeline for large systems 313 Acquiring and retaining large-scale data 314 * Denormalizing and downsampling 316 * Training pitfalls 318 * Reading and encoding data at speed 320 16.4 Integrating a Mahout classifier 324 Plan ahead: key issues for integration 325 * Model serialization 330 16.5 Example: a Thrift-based classification server 332 Running the classification server 336 * Accessing the classifier service 338 16.6 Summary 340

t ^7 Case study: Shop It To Me 341 -/· / 17.1 Why Shop It To Me chose Mahout 342 What Shop It To Me does 342 * Why Shop It To Me needed a classification system 342 * Mahout outscales the rest 343 17.2 General structure of the email marketing system 344 17.3 Training the model 346 Defining the goal of the classification project 346 * Partitioning by time 348 * Avoiding target leaks 348 * Learning algorithm tweaks 348 * Feature vector encoding 349 17.4 Speeding up classification 352 Linear combination of feature vectors 353 * Linear expansion of model score 354 17.5 Summary 356 appendix A JVM tuning 359 appendix B Mahout math 362 appendix C Resources 367 index 369

Review of'Folk Arts of Washington State: A Survey of Contemporary Folk Arts and Artists in the State of Washington'(Lund, 3 pages, 0.14 Mb

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