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## weka.classifiers
Class CostMatrix

    java.lang.Object
      weka.classifiers.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: 1.17 $
Author:
  Mark Hall, Richard Kirkby (rkirkby@cs.waikato.ac.nz)
See Also:
  Serialized Form

Field Summary
`static java.lang.String` | `FILE_EXTENSION` The deafult file extension for cost matrix files

Constructor Summary
`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(java.io.Reader reader)` Reads a matrix from a reader.

Method Summary
`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 Matrix` | `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 Matrix 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`

### 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

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