Package elki.outlier.density

Class IsolationForest

  • All Implemented Interfaces:
    elki.Algorithm, OutlierAlgorithm
    @Reference(authors="F. T. Liu, K. M. Ting, Z.-H. Zhou",
           title="Isolation-Based Anomaly Detection",
           booktitle="Transactions on Knowledge Discovery from Data (TKDD)",
           url="https://doi.org/10.1145/2133360.2133363",
           bibkey="DBLP:journals/tkdd/LiuTZ12")
public class IsolationForest
extends java.lang.Object
implements OutlierAlgorithm
    Isolation-Based Anomaly Detection.

    This method uses an ensemble of randomized trees that serve as a simple density estimator instead of using distances to estimate density.

    Reference:

    F. T. Liu, K. M. Ting, Z.-H. Zhou
    Isolation-Based Anomaly Detection
    Transactions on Knowledge Discovery from Data (TKDD)

    Since:
    0.8.0
    Author:
    Erich Schubert

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      protected static class  IsolationForest.ForestBuilder
      Class to build the forest
      protected static class  IsolationForest.Node
      Minimalistic tree node for the isolation forest.
      static class  IsolationForest.Par
      Parameterization class

      • Nested classes/interfaces inherited from interface elki.Algorithm

        elki.Algorithm.Utils

    • Field Summary

      Fields 
      Modifier and Type Field Description
      private static elki.logging.Logging LOG
      Class logger
      protected int numTrees
      The number of trees
      private elki.utilities.random.RandomFactory rnd
      Random generator
      protected int subsampleSize
      The sub sample size

    • Constructor Summary

      Constructors 
      Constructor Description
      IsolationForest​(int numTrees, int subsampleSize, elki.utilities.random.RandomFactory rnd)
      Constructor.

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      protected static double c​(double n)
      Returns the average path length of an unsuccessful search.
      elki.data.type.TypeInformation[] getInputTypeRestriction()  
      protected double isolationScore​(IsolationForest.Node n, elki.data.NumberVector v)
      Search a vector in the tree, return depth (path length)
      OutlierResult run​(elki.database.relation.Relation<? extends elki.data.NumberVector> relation)
      Run the isolation forest algorithm.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Field Detail

      • LOG

        private static final elki.logging.Logging LOG
        Class logger

      • numTrees

        protected int numTrees
        The number of trees

      • subsampleSize

        protected int subsampleSize
        The sub sample size

      • rnd

        private elki.utilities.random.RandomFactory rnd
        Random generator

    • Constructor Detail

      • IsolationForest

        public IsolationForest​(int numTrees,
                       int subsampleSize,
                       elki.utilities.random.RandomFactory rnd)
        Constructor.
        Parameters:
        numTrees -
        subsampleSize -
        rnd -

    • Method Detail

      • run

        public OutlierResult run​(elki.database.relation.Relation<? extends elki.data.NumberVector> relation)
        Run the isolation forest algorithm.
        Parameters:
        relation - Data relation to index
        Returns:
        Outlier detection result

      • c

        protected static double c​(double n)
        Returns the average path length of an unsuccessful search. Returns 0 if the value is less than or equal to 1.
        Parameters:
        n - Depth
        Returns:
        Expected average

      • isolationScore

        protected double isolationScore​(IsolationForest.Node n,
                                elki.data.NumberVector v)
        Search a vector in the tree, return depth (path length)
        Parameters:
        n - Node to start
        v - Vector to search
        Returns:
        Isolation score based on depth and node size

      • getInputTypeRestriction

        public elki.data.type.TypeInformation[] getInputTypeRestriction()
        Specified by:
        getInputTypeRestriction in interface elki.Algorithm