weka.attributeSelection

Class GreedyStepwise

java.lang.Object

weka.attributeSelection.ASSearch

weka.attributeSelection.GreedyStepwise

All Implemented Interfaces:

Serializable, RankedOutputSearch, StartSetHandler, OptionHandler, RevisionHandler

public class GreedyStepwise
extends ASSearch
implements RankedOutputSearch, StartSetHandler, OptionHandler

GreedyStepwise :

Performs a greedy forward or backward search through the space of attribute subsets. May start with no/all attributes or from an arbitrary point in the space. Stops when the addition/deletion of any remaining attributes results in a decrease in evaluation. Can also produce a ranked list of attributes by traversing the space from one side to the other and recording the order that attributes are selected.

Valid options are:

 -C
  Use conservative forward search

 -B
  Use a backward search instead of a
  forward one.

 -P <start set>
  Specify a starting set of attributes.
  Eg. 1,3,5-7.

 -R
  Produce a ranked list of attributes.

 -T <threshold>
  Specify a theshold by which attributes
  may be discarded from the ranking.
  Use in conjuction with -R

 -N <num to select>
  Specify number of attributes to select

Version:

$Revision: 8034 $

Author:

Mark Hall

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
GreedyStepwise() Constructor

Method Summary

Methods

Modifier and Type	Method and Description
String	conservativeForwardSelectionTipText() Returns the tip text for this property
String	generateRankingTipText() Returns the tip text for this property
int	getCalculatedNumToSelect() Gets the calculated number of attributes to retain.
boolean	getConservativeForwardSelection() Gets whether conservative selection has been enabled
boolean	getGenerateRanking() Gets whether ranking has been requested.
int	getNumToSelect() Gets the number of attributes to be retained.
String[]	getOptions() Gets the current settings of ReliefFAttributeEval.
String	getRevision() Returns the revision string.
boolean	getSearchBackwards() Get whether to search backwards
String	getStartSet() Returns a list of attributes (and or attribute ranges) as a String
double	getThreshold() Returns the threshold so that the AttributeSelection module can discard attributes from the ranking.
String	globalInfo() Returns a string describing this search method
Enumeration	listOptions() Returns an enumeration describing the available options.
String	numToSelectTipText() Returns the tip text for this property
double[][]	rankedAttributes() Produces a ranked list of attributes.
int[]	search(ASEvaluation ASEval, Instances data) Searches the attribute subset space by forward selection.
String	searchBackwardsTipText() Returns the tip text for this property
void	setConservativeForwardSelection(boolean c) Set whether attributes should continue to be added during a forward search as long as merit does not decrease
void	setGenerateRanking(boolean doRank) Records whether the user has requested a ranked list of attributes.
void	setNumToSelect(int n) Specify the number of attributes to select from the ranked list (if generating a ranking).
void	setOptions(String[] options) Parses a given list of options.
void	setSearchBackwards(boolean back) Set whether to search backwards instead of forwards
void	setStartSet(String startSet) Sets a starting set of attributes for the search.
void	setThreshold(double threshold) Set the threshold by which the AttributeSelection module can discard attributes.
String	startSetTipText() Returns the tip text for this property
String	thresholdTipText() Returns the tip text for this property
String	toString() returns a description of the search.

Methods inherited from class weka.attributeSelection.ASSearch

forName, makeCopies

Methods inherited from class java.lang.Object

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

Constructor Detail

GreedyStepwise

public GreedyStepwise()

Constructor

Method Detail

globalInfo

public String globalInfo()

Returns a string describing this search method

Returns:

a description of the search suitable for displaying in the explorer/experimenter gui

searchBackwardsTipText

public String searchBackwardsTipText()

Returns the tip text for this property

Returns:

tip text for this property suitable for displaying in the explorer/experimenter gui

setSearchBackwards

public void setSearchBackwards(boolean back)

Set whether to search backwards instead of forwards

Parameters:

back - true to search backwards

getSearchBackwards

public boolean getSearchBackwards()

Get whether to search backwards

Returns:

true if the search will proceed backwards

thresholdTipText

public String thresholdTipText()

Returns the tip text for this property

Returns:

tip text for this property suitable for displaying in the explorer/experimenter gui

setThreshold

public void setThreshold(double threshold)

Set the threshold by which the AttributeSelection module can discard attributes.

Specified by:

setThreshold in interface RankedOutputSearch

Parameters:

threshold - the threshold.

getThreshold

public double getThreshold()

Returns the threshold so that the AttributeSelection module can discard attributes from the ranking.

Specified by:

getThreshold in interface RankedOutputSearch

Returns:

a threshold by which to discard attributes

numToSelectTipText

public String numToSelectTipText()

Returns the tip text for this property

Returns:

tip text for this property suitable for displaying in the explorer/experimenter gui

setNumToSelect

public void setNumToSelect(int n)

Specify the number of attributes to select from the ranked list (if generating a ranking). -1 indicates that all attributes are to be retained.

Specified by:

setNumToSelect in interface RankedOutputSearch

Parameters:

n - the number of attributes to retain

getNumToSelect

public int getNumToSelect()

Gets the number of attributes to be retained.

Specified by:

getNumToSelect in interface RankedOutputSearch

Returns:

the number of attributes to retain

getCalculatedNumToSelect

public int getCalculatedNumToSelect()

Gets the calculated number of attributes to retain. This is the actual number of attributes to retain. This is the same as getNumToSelect if the user specifies a number which is not less than zero. Otherwise it should be the number of attributes in the (potentially transformed) data.

Specified by:

getCalculatedNumToSelect in interface RankedOutputSearch

generateRankingTipText

public String generateRankingTipText()

Returns the tip text for this property

Returns:

tip text for this property suitable for displaying in the explorer/experimenter gui

setGenerateRanking

public void setGenerateRanking(boolean doRank)

Records whether the user has requested a ranked list of attributes.

Specified by:

setGenerateRanking in interface RankedOutputSearch

Parameters:

doRank - true if ranking is requested

getGenerateRanking

public boolean getGenerateRanking()

Gets whether ranking has been requested. This is used by the AttributeSelection module to determine if rankedAttributes() should be called.

Specified by:

getGenerateRanking in interface RankedOutputSearch

Returns:

true if ranking has been requested.

startSetTipText

public String startSetTipText()

Returns the tip text for this property

Returns:

tip text for this property suitable for displaying in the explorer/experimenter gui

setStartSet

public void setStartSet(String startSet)
                 throws Exception

Sets a starting set of attributes for the search. It is the search method's responsibility to report this start set (if any) in its toString() method.

Specified by:

setStartSet in interface StartSetHandler

Parameters:

startSet - a string containing a list of attributes (and or ranges), eg. 1,2,6,10-15.

Throws:

Exception - if start set can't be set.

getStartSet

public String getStartSet()

Returns a list of attributes (and or attribute ranges) as a String

Specified by:

getStartSet in interface StartSetHandler

Returns:

a list of attributes (and or attribute ranges)

conservativeForwardSelectionTipText

public String conservativeForwardSelectionTipText()

Returns the tip text for this property

Returns:

tip text for this property suitable for displaying in the explorer/experimenter gui

setConservativeForwardSelection

public void setConservativeForwardSelection(boolean c)

Set whether attributes should continue to be added during a forward search as long as merit does not decrease

Parameters:

c - true if atts should continue to be atted

getConservativeForwardSelection

public boolean getConservativeForwardSelection()

Gets whether conservative selection has been enabled

Returns:

true if conservative forward selection is enabled

listOptions

public Enumeration listOptions()

Returns an enumeration describing the available options.

Specified by:

listOptions in interface OptionHandler

Returns:

an enumeration of all the available options.

setOptions

public void setOptions(String[] options)
                throws Exception

Parses a given list of options.

Valid options are:

 -C
  Use conservative forward search

 -B
  Use a backward search instead of a
  forward one.

 -P <start set>
  Specify a starting set of attributes.
  Eg. 1,3,5-7.

 -R
  Produce a ranked list of attributes.

 -T <threshold>
  Specify a theshold by which attributes
  may be discarded from the ranking.
  Use in conjuction with -R

 -N <num to select>
  Specify number of attributes to select

Specified by:

setOptions in interface OptionHandler

Parameters:

options - the list of options as an array of strings

Throws:

Exception - if an option is not supported

getOptions

public String[] getOptions()

Gets the current settings of ReliefFAttributeEval.

Specified by:

getOptions in interface OptionHandler

Returns:

an array of strings suitable for passing to setOptions()

toString

public String toString()

returns a description of the search.

Overrides:

toString in class Object

Returns:

a description of the search as a String.

search

public int[] search(ASEvaluation ASEval,
           Instances data)
             throws Exception

Searches the attribute subset space by forward selection.

Specified by:

search in class ASSearch

Parameters:

ASEval - the attribute evaluator to guide the search

data - the training instances.

Returns:

an array (not necessarily ordered) of selected attribute indexes

Throws:

Exception - if the search can't be completed

rankedAttributes

public double[][] rankedAttributes()
                            throws Exception

Produces a ranked list of attributes. Search must have been performed prior to calling this function. Search is called by this function to complete the traversal of the the search space. A list of attributes and merits are returned. The attributes a ranked by the order they are added to the subset during a forward selection search. Individual merit values reflect the merit associated with adding the corresponding attribute to the subset; because of this, merit values may initially increase but then decrease as the best subset is "passed by" on the way to the far side of the search space.

Specified by:

rankedAttributes in interface RankedOutputSearch

Returns:

an array of attribute indexes and associated merit values

Throws:

Exception - if something goes wrong.

getRevision

public String getRevision()

Returns the revision string.

Specified by:

getRevision in interface RevisionHandler

Overrides:

getRevision in class ASSearch

Returns:

the revision