weka.classifiers

Class CostMatrix

java.lang.Object

weka.classifiers.CostMatrix

All Implemented Interfaces:

Serializable, RevisionHandler

public class CostMatrix
extends Object
implements 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: 10141 $

Author:

Mark Hall, Richard Kirkby (rkirkby@cs.waikato.ac.nz)

See Also:

Serialized Form

Field Summary

Fields

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

Constructor Summary

Constructors

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

Method Summary

Methods

Modifier and Type	Method and Description
Instances	applyCostMatrix(Instances data, 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.
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.
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(String matlab) creates a matrix from the given Matlab string.
void	readOldFormat(Reader reader) Loads a cost matrix in the old format from a reader.
void	setCell(int rowIndex, int columnIndex, 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)
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].
String	toString() Converts a matrix to a string.
void	write(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 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(Reader reader)
           throws 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:

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,
                        Random random)
                          throws 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:

Exception - if the data has no class or the matrix in inappropriate.

expectedCosts

public double[] expectedCosts(double[] classProbs)
                       throws 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:

Exception - if the wrong number of class probabilities is supplied.

expectedCosts

public double[] expectedCosts(double[] classProbs,
                     Instance inst)
                       throws 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:

Exception - if something goes wrong

getMaxCost

public double getMaxCost(int classVal)
                  throws Exception

Gets the maximum cost for a particular class value.

Parameters:

classVal - the class value.

Returns:

the maximum cost.

Throws:

Exception - if cost matrix contains non-fixed costs

getMaxCost

public double getMaxCost(int classVal,
                Instance inst)
                  throws Exception

Gets the maximum cost for a particular class value.

Parameters:

classVal - the class value.

Returns:

the maximum cost.

Throws:

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(Reader reader)
                   throws 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:

Exception - if the matrix cannot be read correctly.

write

public void write(Writer w)
           throws 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:

Exception - if an error occurs

toMatlab

public 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

parseMatlab

public static CostMatrix parseMatlab(String matlab)
                              throws 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:

Exception

See Also:

toMatlab()

setCell

public final void setCell(int rowIndex,
           int columnIndex,
           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 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 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:

Exception - if the value is not a double

getElement

public final double getElement(int rowIndex,
                int columnIndex,
                Instance inst)
                        throws 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:

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

toString

public String toString()

Converts a matrix to a string. (FracPete: taken from old weka.core.Matrix class)

Overrides:

toString in class Object

Returns:

the converted string

getRevision

public String getRevision()

Returns the revision string.

Specified by:

getRevision in interface RevisionHandler

Returns:

the revision