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An Introduction To Weka


An Introduction To Weka

An Introduction To Weka

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  • Talk about * hacking weka * discretization * cross validations
  • Simple CLI provides a commandline interface to weka’s routines Explorer interface provides a graphical front end to weka’s routines and components Experimenter allows you to build classification experiments KnowledgeFlow provides an alternative to the Explorer as a graphical front end to Weka's core algorithms.


  • 1. Weka: A Short Introduction
  • 2. Introduction
    • A collection of open source ML algorithms
      • pre-processing
      • classifiers
      • clustering
      • association rule
    • Created by researchers at the University of Waikato in New Zealand
    • Software Platform: Java based
  • 3. What is WEKA
    • Waikato Environment for Knowledge Analysis (WEKA)
    • Developed by the Department of Computer Science, University of Waikato, New Zealand
    • Machine learning/data mining software written in Java (distributed under the GNU Public License)
    • Used for research, education, and applications
  • 4. Installation
    • Download software from
      • If you are interested in modifying/extending weka there is a developer version that includes the source code
    • Set the weka environment variable for java
    • Download some ML data from
  • 5. Main Features
    • 49 data preprocessing tools
    • 76 classification/regression algorithms
    • 8 clustering algorithms
    • 15 attribute/subset evaluators + 10 search algorithms for feature selection
    • 3 algorithms for finding association rules
    • More algorithms being added
    • Options to customize using the Java source code is made available.
    • Custom extensions and plug ins can be developed
    • Excellent mailing and discussion lists available.
    • 3 graphical user interfaces
      • “ The Explorer” (exploratory data analysis)
      • “ The Experimenter” (experimental environment)
      • “ The KnowledgeFlow” (new process model inspired interface)
  • 6. Weka Interfaces
    • Command-line
    • Explorer
      • preprocessing, attribute selection, learning, visualiation
    • Knowledge Flow
      • visual design of KDD process
      • capabilities ~ Explorer
    • Experimenter
      • testing and evaluating machine learning algorithms
  • 7. WEKA GUI Interface
  • 8. WEKA Data format
    • Uses flat text files to describe the data
    • Can work with a wide variety of data files including its own “.arff” format and C4.5 file formats
    • 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)
  • 9. WEKA:: ARRF file format
    • @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
    • ...
    numeric attribute nominal attribute
  • 10. Attribute-Relation File Format (ARFF)
    • Weka reads ARFF files:
        • @relation adult @attribute age numeric @attribute name string @attribute education {College, Masters, Doctorate} @attribute class {>50K,<=50K} @data
        • 50,Lisa, College, <= 50K 30,Martin John, College,<=50K
    • Supported attributes:
      • numeric, nominal, string, date
    • Details at:
  • 11. Weka Explorer
    • What we will use today in Weka:
    • Pre-process:
      • Load, analyze, and filter data
    • Visualize:
      • Compare pairs of attributes
      • Plot matrices
    • Classify:
      • All algorithms seem in class (Naive Bayes, etc.)
    • Feature selection:
      • Forward feature subset selection, etc.
  • 12. 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 databases using JDBC
    • Pre-processing tools in WEKA are called “filters”
    • WEKA contains filters for:
      • Discretization, normalization, resampling, attribute selection, attribute combination, …
  • 13. Explorer: Building classification models
    • “ Classifiers” in WEKA are models for predicting nominal or numeric quantities
    • Implemented schemes include:
      • Decision trees and lists, instance-based classifiers, support vector machines, multi-layer perceptrons, logistic regression, Bayes’ nets, …
    • “ Meta”-classifiers include:
      • Bagging, boosting, stacking, error-correcting output codes, data cleansing, …
  • 14. load filter analyze
  • 15. visualize attributes
  • 16. Weka Experimenter
    • If you need to perform many experiments:
      • Experimenter makes it easy to compare the performance of different learning schemes
      • Results can be written into file or database
      • Evaluation options: cross-validation, learning curve, etc.
      • Can also iterate over different parameter settings
      • Significance-testing built in .
  • 17. Visit more self help tutorials
    • Pick a tutorial of your choice and browse through it at your own pace.
    • The tutorials section is free, self-guiding and will not involve any additional support.
    • Visit us at