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Weka presentation Weka presentation Presentation Transcript

  • An Introduction to WEKA Saeed Iqbal
  • Content What is WEKA? Data set in WEKA The Explorer: Preprocess data Classification Clustering Association Rules Attribute Selection Data Visualization References and Resources2 01/07/13
  • What is WEKA? Waikato Environment for Knowledge Analysis It’s a data mining/machine learning tool developed by Department of Computer Science, University of Waikato, New Zealand. Weka is a collection of machine learning algorithms for data mining tasks. Weka is open source software issued under the GNU General Public License.3 01/07/13
  • Download and Install WEKA Website: http://www.cs.waikato.ac.nz/~ml/weka/index.html Support multiple platforms (written in java):  Windows, Mac OS X and Linux Weka Manual: http://transact.dl.sourceforge.net/sourcefor ge/weka/WekaManual-3.6.0.pdf4 01/07/13
  • Main Features 49 data preprocessing tools 76 classification/regression algorithms 8 clustering algorithms 3 algorithms for finding association rules 15 attribute/subset evaluators + 10 search algorithms for feature selection5 01/07/13
  • Main GUI  Three graphical user interfaces “The Explorer” (exploratory data analysis) “The Experimenter” (experimental environment) “The KnowledgeFlow” (new process model inspired interface) Simple CLI (Command prompt)  Offers some functionality not available via the GUI6 01/07/13
  • Datasets in WekaEach entry in a dataset is an instance of the java class: weka.core.InstanceEach instance consists of a number of attributes Nominal: one of a predefined list of values  e.g. red, green, blue Numeric: A real or integer number String: Enclosed in “double quotes” Date Relational
  • ARFF FilesWeka wants its input data in ARFF format. A dataset has to start with a declaration of its name:  @relation name @attribute attribute_name specification  If an attribute is nominal, specification contains a list of the possible attribute values in curly brackets:  @attribute nominal_attribute {first_value, second_value, third_value}  If an attribute is numeric, specification is replaced by the keyword numeric: (Integer values are treated as real numbers in WEKA.)  @attribute numeric_attribute numeric After the attribute declarations, the actual data is introduced by a tag:  @data
  • ARFF File@relation weather@attribute outlook { sunny, overcast, rainy }@attribute temperature numeric@attribute humidity numeric@attribute windy { TRUE, FALSE }@attribute play { yes, no }@datasunny, 85, 85, FALSE, nosunny, 80, 90, TRUE, noovercast, 83, 86, FALSE, yesrainy, 70, 96, FALSE, yesrainy, 68, 80, FALSE, yesrainy, 65, 70, TRUE, noovercast, 64, 65, TRUE, yessunny, 72, 95, FALSE, nosunny, 69, 70, FALSE, yesrainy, 75, 80, FALSE, yessunny, 75, 70, TRUE, yesovercast, 72, 90, TRUE, yesovercast, 81, 75, FALSE, yesrainy, 71, 91, TRUE, no
  • WEKA: ExplorerPreprocess: Choose and modify the data being acted on.Classify: Train and test learning schemes that classify or perform regression.Cluster: Learn clusters for the data.Associate: Learn association rules for the data.Select attributes: Select the most relevant attributes in the data.Visualize: View an interactive 2D plot of the data.
  • Content What is WEKA? Data set in WEKA The Explorer: Preprocess data Classification Clustering Association Rules Attribute Selection Data Visualization References and Resources11 01/07/13
  • Explorer: pre-processing the data Data can be imported from a file in various formats: ARFF, CSV, C4.5, binary Data can also be read from a URL or from an SQL database (using JDBC) Pre-processing tools in WEKA are called “filters” WEKA contains filters for: Discretization, normalization, resampling, attribute selection, transforming and combining attributes, …12 01/07/13
  • WEKA only deals with “flat” files @relation heart-disease-simplified @attribute age numeric @attribute sex { female, male} @attribute chest_pain_type { typ_angina, asympt, non_anginal, atyp_angina} @attribute cholesterol numeric @attribute exercise_induced_angina { no, yes} @attribute class { present, not_present} @data 63,male,typ_angina,233,no,not_present 67,male,asympt,286,yes,present 67,male,asympt,229,yes,present 38,female,non_anginal,?,no,not_present ...13 01/07/13
  • WEKA only deals with “flat” files @relation heart-disease-simplified @attribute age numeric @attribute sex { female, male} @attribute chest_pain_type { typ_angina, asympt, non_anginal, atyp_angina} @attribute cholesterol numeric @attribute exercise_induced_angina { no, yes} @attribute class { present, not_present} @data 63,male,typ_angina,233,no,not_present 67,male,asympt,286,yes,present 67,male,asympt,229,yes,present 38,female,non_anginal,?,no,not_present ...14 01/07/13
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  • Explorer: building “classifiers” Classifiers in WEKA are models for predicting nominal or numeric quantities Implemented learning schemes include: Decision trees and lists, instance-based classifiers, support vector machines, multi-layer perceptrons, logistic regression, Bayes’ nets, …36 01/07/13
  • Decision Tree Induction: Training Dataset age income student credit_rating buys_computer <=30 high no fair noThis follows <=30 high no excellent no 31…40 high no fair yesan example >40 medium no fair yesof Quinlan’s >40 low yes fair yesID3 (Playing >40 low yes excellent no 31…40 low yes excellent yesTennis) <=30 medium no fair no <=30 low yes fair yes >40 medium yes fair yes <=30 medium yes excellent yes 31…40 medium no excellent yes 31…40 high yes fair yes >40 medium no excellent no37 January 7, 2013
  • Output: A Decision Tree for “buys_computer” age? <=30 overcast 31..40 >40 student? yes credit rating? no yes excellent fair no yes no yes38 January 7, 2013
  • Algorithm for Decision Tree Induction  Basic algorithm (a greedy algorithm) Tree is constructed in a top-down recursive divide-and-conquer manner At start, all the training examples are at the root Attributes are categorical (if continuous-valued, they are discretized in advance) Examples are partitioned recursively based on selected attributes Test attributes are selected on the basis of a heuristic or statistical measure (e.g., information gain)39 January 7, 2013
  • classifiers DEMO
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  • Explorer: clustering data WEKA contains “clusterers” for finding groups of similar instances in a dataset Implemented schemes are: k-Means, EM, Cobweb, X-means, FarthestFirst Clusters can be visualized and compared to “true” clusters (if given) Evaluation based on loglikelihood if clustering scheme produces a probability distribution63 01/07/13
  • Clustering DEMO
  • The K-Means Clustering Method  Given k, the k-means algorithm is implemented in four steps: Partition objects into k nonempty subsets Compute seed points as the centroids of the clusters of the current partition (the centroid is the center, i.e., mean point, of the cluster) Assign each object to the cluster with the nearest seed point Go back to Step 2, stop when no more new assignment65 January 7, 2013
  • Explorer: finding associations WEKA contains an implementation of the Apriori algorithm for learning association rules Works only with discrete data Can identify statistical dependencies between groups of attributes: milk, butter ⇒ bread, eggs (with confidence 0.9 and support 2000) Apriori can compute all rules that have a given minimum support and exceed a given confidence66 01/07/13
  • Basic Concepts: Frequent PatternsTid Items bought  itemset: A set of one or more items10 Beer, Nuts, Diaper  k-itemset X = {x1, …, xk}20 Beer, Coffee, Diaper  (absolute) support, or, support count of X:30 Beer, Diaper, Eggs Frequency or occurrence of an itemset40 Nuts, Eggs, Milk X50 Nuts, Coffee, Diaper, Eggs, Milk  (relative) support, s, is the fraction of Customer Customer transactions that contains X (i.e., the buys both buys diaper probability that a transaction contains X)  An itemset X is frequent if X’s support is no less than a minsup threshold Customer buys beer67 January 7, 2013
  • Basic Concepts: Association RulesTid Items bought  Find all the rules X  Y with minimum10 Beer, Nuts, Diaper support and confidence20 Beer, Coffee, Diaper30 Beer, Diaper, Eggs  support, s, probability that a40 Nuts, Eggs, Milk transaction contains X ∪ Y50 Nuts, Coffee, Diaper, Eggs, Milk  confidence, c, conditional probability Customer Customer that a transaction having X also buys both buys contains Y diaper Let minsup = 50%, minconf = 50% Freq. Pat.: Beer:3, Nuts:3, Diaper:4, Eggs:3, {Beer, Diaper}:3 Customer buys beer  Association rules: (many more!)  Beer  Diaper (60%, 100%)  Diaper  Beer (60%, 75%)68 January 7, 2013
  • Association DEMO
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  • Explorer: attribute selection Panel that can be used to investigate which (subsets of) attributes are the most predictive ones Attribute selection methods contain two parts: A search method: best-first, forward selection, random, exhaustive, genetic algorithm, ranking An evaluation method: correlation-based, wrapper, information gain, chi-squared, … Very flexible: WEKA allows (almost) arbitrary combinations of these two75 01/07/13
  • Explorer: attribute selection DEMO
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  • Explorer: data visualization Visualization very useful in practice: e.g. helps to determine difficulty of the learning problem WEKA can visualize single attributes (1-d) and pairs of attributes (2-d) To do: rotating 3-d visualizations (Xgobi-style) Color-coded class values “Jitter” option to deal with nominal attributes (and to detect “hidden” data points) “Zoom-in” function85 01/07/13
  • data visualization DEMO
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  • References and Resources References: WEKA website: http://www.cs.waikato.ac.nz/~ml/weka/index.html WEKA Tutorial:  Machine Learning with WEKA: A presentation demonstrating all graphical user interfaces (GUI) in Weka.  A presentation which explains how to use Weka for exploratory data mining. WEKA Data Mining Book:  Ian H. Witten and Eibe Frank, Data Mining: Practical Machine Learning Tools and Techniques (Second Edition) WEKA Wiki: http://weka.sourceforge.net/wiki/index.php/Main_Page Others:  Jiawei Han and Micheline Kamber, Data Mining: Concepts and Techniques, 2nd ed.