Mahout part2
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Part two of a presentation about Mahout system. It is based on http://my.safaribooksonline.com/9781935182689/

Part two of a presentation about Mahout system. It is based on http://my.safaribooksonline.com/9781935182689/

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Mahout part2 Mahout part2 Presentation Transcript

  • Mahout in Action Part 2 Yasmine M. Gaber 4 April 2013
  • Agenda Part 2: Clustering Part 3: Classification
  • Clustering An algorithm A notion of both similarity and dissimilarity A stopping condition
  • Measuring the similarity of items Euclidean Distance
  • Creating the input Preprocess the data Use that data to create vectors Save the vectors in SequenceFile format as input for the algorithm
  • Using Mahout clustering The SequenceFile containing the input vectors. The SequenceFile containing the initial cluster centers. The similarity measure to be used. The convergenceThreshold. The number of iterations to be done. The Vector implementation used in the input files.
  • Using Mahout clustering
  • Distance measures Euclidean distance measure Squared Euclidean distance measure Manhattan distance measure
  • Distance measures Cosine distance measure Tanimoto distance measure
  • Playing Around
  • Representing data
  • Representing text documents as vectors Vector Space Model (VSM) TF-IDF N-gram collocations
  • Generating vectors from documents $ bin/mahout seqdirectory -c UTF-8 -i examples/reuters-extracted/ -o reuters-seqfiles $ bin/mahout seq2sparse -i reuters-seqfiles/ -o reuters-vectors -ow
  • Improving quality of vectors using normalization P-norm $ bin/mahout seq2sparse -i reuters-seqfiles/ -o reuters-normalized-bigram -ow -a org.apache.lucene.analysis.WhitespaceAnalyz er-chunk 200 -wt tfidf -s 5 -md 3 -x 90 -ng 2 -ml 50 -seq -n 2
  • Clustering Categories Exclusive clustering Overlapping clustering Hierarchical clustering Probabilistic clustering
  • Clustering Approaches Fixed number of centers Bottom-up approach Top-down approach
  • Clustering algorithms K-means clustering Fuzzy k-means clustering Dirichlet clustering
  • k-means clustering algorithm
  • Running k-means clustering
  • Running k-means clustering $ bin/mahout kmeans -i reuters-vectors/tfidf- vectors/ -c reuters-initial-clusters -o reuters- kmeans-clusters -dm org.apache.mahout.common.distance.Square dEuclideanDistanceMeasure -cd 1.0 -k 20 -x 20 -cl $ bin/mahout kmeans -i reuters-vectors/tfidf- vectors/ -c reuters-initial-clusters -o reuters- kmeans-clusters -dm org.apache.mahout.common.distance.Cosine DistanceMeasure -cd 0.1 -k 20 -x 20 -cl $ bin/mahout clusterdump -dt sequencefile -d
  • Fuzzy k-means clustering Instead of the exclusive clustering in k-means, fuzzy k-means tries to generate overlapping clusters from the data set. Also known as fuzzy c-means algorithm.
  • Running fuzzy k-means clustering
  • Running fuzzy k-means clustering $ bin/mahout fkmeans -i reuters-vectors/tfidf- vectors/ -c reuters-fkmeans-centroids -o reuters-fkmeans-clusters -cd 1.0 -k 21 -m 2 -ow -x 10 -dm org.apache.mahout.common.distance.Square dEuclideanDistanceMeasure Fuzziness factor
  • Dirichlet clustering model-based clustering algorithm
  • Running Dirichlet clustering $ bin/mahout dirichlet -i reuters-vectors/tfidf- vectors -o reuters-dirichlet-clusters -k 60 -x 10 -a0 1.0 -md org.apache.mahout.clustering.dirichlet.models. GaussianClusterDistribution -mp org.apache.mahout.math.SequentialAccessSp arseVector
  • Evaluating and improving clustering quality Inspecting clustering output Evaluating the quality of clustering0 Improving clustering quality
  • Inspecting clustering output $ bin/mahout clusterdump -s kmeans- output/clusters-19/ -d reuters- vectors/dictionary.file-0 -dt sequencefile -n 10 Top Terms: said => 11.60126582278481 bank => 5.943037974683544 dollar =>
  • Analyzing clustering output Distance measure and feature selection Inter-cluster and intra-cluster distances Mixed and overlapping clusters
  • Improving clustering quality Improving document vector generation Writing a custom distance measure
  • Real-world applications of clustering Clustering like-minded people on Twitter Suggesting tags for an artist on Last.fm using clustering Creating a related-posts feature for a website
  • Classification Classification is a process of using specific information (input) to choose a single selection (output) from a short list of predetermined potential responses. Applications of classification, e.g. spam filtering
  • Why use Mahout for classification?
  • How classification works
  • Classification Training versus test versus production Predictor variables versus target variable Records, fields, and values
  • Types of values for predictor variables Continuous Categorical Word-like Text-like
  • Classification Work flow Training the model Evaluating the model Using the model in production
  • Stage 1: training the classification modelStage 2: evaluating the classification modelStage 3: using the model in production
  • Stage 1: training the classification model Define Categories for the Target Variable Collect Historical Data Define Predictor Variables Select a Learning Algorithm to Train the Model Use Learning Algorithm to Train the Model
  • Extracting features to build a Mahout classifier
  • Preprocessing raw data into classifiable data
  • Converting classifiable data into vectors Use one Vector cell per word, category, or continuous value Represent Vectors implicitly as bags of words Use feature hashing
  • Classifying the 20 newsgroups data set
  • Choosing an algorithm
  • The classifier evaluation API Percent correct Confusion matrix Entropy matrix AUC Log likelihood
  • When classifiers go bad Target leaks Broken feature extraction
  • Tuning the problem Remove Fluff Variables Add New Variables, Interactions, and Derived Values
  • Tuning the classifier Try Alternative Algorithms Tune the Learning Algorithm
  • Thank You Contact at:Email: Yasmine.Gaber@espace.com.egTwitter: Twitter.com/yasmine_mohamed