Package weka.classifiers

Class CostMatrix

  • All Implemented Interfaces:
    java.io.Serializable, RevisionHandler
    public class CostMatrix
extends java.lang.Object
implements java.io.Serializable, RevisionHandler
    Class for storing and manipulating a misclassification cost matrix. The element at position i,j in the matrix is the penalty for classifying an instance of class j as class i. Cost values can be fixed or computed on a per-instance basis (cost sensitive evaluation only) from the value of an attribute or an expression involving attribute(s).
    Version:
    $Revision: 9048 $
    Author:
    Mark Hall, Richard Kirkby (rkirkby@cs.waikato.ac.nz)
    See Also:
    Serialized Form

    • Field Summary

      Fields 
      Modifier and Type Field Description
      static java.lang.String FILE_EXTENSION
      The deafult file extension for cost matrix files

    • Constructor Summary

      Constructors 
      Constructor Description
      CostMatrix​(int numOfClasses)
      Creates a default cost matrix of a particular size.
      CostMatrix​(java.io.Reader reader)
      Reads a matrix from a reader.
      CostMatrix​(CostMatrix toCopy)
      Creates a cost matrix that is a copy of another.

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      Instances applyCostMatrix​(Instances data, java.util.Random random)
      Applies the cost matrix to a set of instances.
      double[] expectedCosts​(double[] classProbs)
      Calculates the expected misclassification cost for each possible class value, given class probability estimates.
      double[] expectedCosts​(double[] classProbs, Instance inst)
      Calculates the expected misclassification cost for each possible class value, given class probability estimates.
      java.lang.Object getCell​(int rowIndex, int columnIndex)
      Return the contents of a particular cell.
      double getElement​(int rowIndex, int columnIndex)
      Return the value of a cell as a double (for legacy code)
      double getElement​(int rowIndex, int columnIndex, Instance inst)
      Return the value of a cell as a double.
      double getMaxCost​(int classVal)
      Gets the maximum cost for a particular class value.
      double getMaxCost​(int classVal, Instance inst)
      Gets the maximum cost for a particular class value.
      java.lang.String getRevision()
      Returns the revision string.
      void initialize()
      Initializes the matrix
      void normalize()
      Normalizes the matrix so that the diagonal contains zeros.
      int numColumns()
      Same as size
      int numRows()
      Same as size
      static CostMatrix parseMatlab​(java.lang.String matlab)
      creates a matrix from the given Matlab string.
      void readOldFormat​(java.io.Reader reader)
      Loads a cost matrix in the old format from a reader.
      void setCell​(int rowIndex, int columnIndex, java.lang.Object value)
      Set the value of a particular cell in the matrix
      void setElement​(int rowIndex, int columnIndex, double value)
      Set the value of a cell as a double
      int size()
      The number of rows (and columns)
      java.lang.String toMatlab()
      converts the Matrix into a single line Matlab string: matrix is enclosed by parentheses, rows are separated by semicolon and single cells by blanks, e.g., [1 2; 3 4].
      java.lang.String toString()
      Converts a matrix to a string.
      void write​(java.io.Writer w)
      Writes out a matrix.

      • Methods inherited from class java.lang.Object

        equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

    • Field Detail

      • FILE_EXTENSION

        public static java.lang.String FILE_EXTENSION
        The deafult file extension for cost matrix files

    • Constructor Detail

      • CostMatrix

        public CostMatrix​(int numOfClasses)
        Creates a default cost matrix of a particular size. All diagonal values will be 0 and all non-diagonal values 1.
        Parameters:
        numOfClasses - the number of classes that the cost matrix holds.

      • CostMatrix

        public CostMatrix​(CostMatrix toCopy)
        Creates a cost matrix that is a copy of another.
        Parameters:
        toCopy - the matrix to copy.

      • CostMatrix

        public CostMatrix​(java.io.Reader reader)
           throws java.lang.Exception
        Reads a matrix from a reader. The first line in the file should contain the number of rows and columns. Subsequent lines contain elements of the matrix. (FracPete: taken from old weka.core.Matrix class)
        Parameters:
        reader - the reader containing the matrix
        Throws:
        java.lang.Exception - if an error occurs
        See Also:
        write(Writer)

    • Method Detail

      • initialize

        public void initialize()
        Initializes the matrix

      • size

        public int size()
        The number of rows (and columns)
        Returns:
        the size of the matrix

      • numColumns

        public int numColumns()
        Same as size
        Returns:
        the number of columns

      • numRows

        public int numRows()
        Same as size
        Returns:
        the number of rows

      • applyCostMatrix

        public Instances applyCostMatrix​(Instances data,
                                 java.util.Random random)
                          throws java.lang.Exception
        Applies the cost matrix to a set of instances. If a random number generator is supplied the instances will be resampled, otherwise they will be rewighted. Adapted from code once sitting in Instances.java
        Parameters:
        data - the instances to reweight.
        random - a random number generator for resampling, if null then instances are rewighted.
        Returns:
        a new dataset reflecting the cost of misclassification.
        Throws:
        java.lang.Exception - if the data has no class or the matrix in inappropriate.

      • expectedCosts

        public double[] expectedCosts​(double[] classProbs)
                       throws java.lang.Exception
        Calculates the expected misclassification cost for each possible class value, given class probability estimates.
        Parameters:
        classProbs - the class probability estimates.
        Returns:
        the expected costs.
        Throws:
        java.lang.Exception - if the wrong number of class probabilities is supplied.

      • expectedCosts

        public double[] expectedCosts​(double[] classProbs,
                              Instance inst)
                       throws java.lang.Exception
        Calculates the expected misclassification cost for each possible class value, given class probability estimates.
        Parameters:
        classProbs - the class probability estimates.
        inst - the current instance for which the class probabilites apply. Is used for computing any non-fixed cost values.
        Returns:
        the expected costs.
        Throws:
        java.lang.Exception - if something goes wrong

      • getMaxCost

        public double getMaxCost​(int classVal)
                  throws java.lang.Exception
        Gets the maximum cost for a particular class value.
        Parameters:
        classVal - the class value.
        Returns:
        the maximum cost.
        Throws:
        java.lang.Exception - if cost matrix contains non-fixed costs

      • getMaxCost

        public double getMaxCost​(int classVal,
                         Instance inst)
                  throws java.lang.Exception
        Gets the maximum cost for a particular class value.
        Parameters:
        classVal - the class value.
        Returns:
        the maximum cost.
        Throws:
        java.lang.Exception - if cost matrix contains non-fixed costs

      • normalize

        public void normalize()
        Normalizes the matrix so that the diagonal contains zeros.

      • readOldFormat

        public void readOldFormat​(java.io.Reader reader)
                   throws java.lang.Exception
        Loads a cost matrix in the old format from a reader. Adapted from code once sitting in Instances.java
        Parameters:
        reader - the reader to get the values from.
        Throws:
        java.lang.Exception - if the matrix cannot be read correctly.

      • write

        public void write​(java.io.Writer w)
           throws java.lang.Exception
        Writes out a matrix. The format can be read via the CostMatrix(Reader) constructor. (FracPete: taken from old weka.core.Matrix class)
        Parameters:
        w - the output Writer
        Throws:
        java.lang.Exception - if an error occurs

      • toMatlab

        public java.lang.String toMatlab()
        converts the Matrix into a single line Matlab string: matrix is enclosed by parentheses, rows are separated by semicolon and single cells by blanks, e.g., [1 2; 3 4].
        Returns:
        the matrix in Matlab single line format

      • setCell

        public final void setCell​(int rowIndex,
                          int columnIndex,
                          java.lang.Object value)
        Set the value of a particular cell in the matrix
        Parameters:
        rowIndex - the row
        columnIndex - the column
        value - the value to set

      • getCell

        public final java.lang.Object getCell​(int rowIndex,
                                      int columnIndex)
        Return the contents of a particular cell. Note: this method returns the Object stored at a particular cell.
        Parameters:
        rowIndex - the row
        columnIndex - the column
        Returns:
        the value at the cell

      • getElement

        public final double getElement​(int rowIndex,
                               int columnIndex)
                        throws java.lang.Exception
        Return the value of a cell as a double (for legacy code)
        Parameters:
        rowIndex - the row
        columnIndex - the column
        Returns:
        the value at a particular cell as a double
        Throws:
        java.lang.Exception - if the value is not a double

      • getElement

        public final double getElement​(int rowIndex,
                               int columnIndex,
                               Instance inst)
                        throws java.lang.Exception
        Return the value of a cell as a double. Computes the value for non-fixed costs using the supplied Instance
        Parameters:
        rowIndex - the row
        columnIndex - the column
        Returns:
        the value from a particular cell
        Throws:
        java.lang.Exception - if something goes wrong

      • setElement

        public final void setElement​(int rowIndex,
                             int columnIndex,
                             double value)
        Set the value of a cell as a double
        Parameters:
        rowIndex - the row
        columnIndex - the column
        value - the value (double) to set

      • parseMatlab

        public static CostMatrix parseMatlab​(java.lang.String matlab)
                              throws java.lang.Exception
        creates a matrix from the given Matlab string.
        Parameters:
        matlab - the matrix in matlab format
        Returns:
        the matrix represented by the given string
        Throws:
        java.lang.Exception
        See Also:
        toMatlab()

      • toString

        public java.lang.String toString()
        Converts a matrix to a string. (FracPete: taken from old weka.core.Matrix class)
        Overrides:
        toString in class java.lang.Object
        Returns:
        the converted string

      • getRevision

        public java.lang.String getRevision()
        Returns the revision string.
        Specified by:
        getRevision in interface RevisionHandler
        Returns:
        the revision