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## weka.attributeSelection
Class GreedyStepwise

    java.lang.Object
      weka.attributeSelection.ASSearch
          weka.attributeSelection.GreedyStepwise

All Implemented Interfaces:
  java.io.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: 7267 $
Author:
  Mark Hall
See Also:
  Serialized Form

Constructor Summary
`GreedyStepwise()` Constructor

Method Summary
`java.lang.String` | `conservativeForwardSelectionTipText()` Returns the tip text for this property
`java.lang.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.
`java.lang.String[]` | `getOptions()` Gets the current settings of ReliefFAttributeEval.
`java.lang.String` | `getRevision()` Returns the revision string.
`boolean` | `getSearchBackwards()` Get whether to search backwards
`java.lang.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.
`java.lang.String` | `globalInfo()` Returns a string describing this search method
`java.util.Enumeration` | `listOptions()` Returns an enumeration describing the available options.
`java.lang.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.
`java.lang.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(java.lang.String[] options)` Parses a given list of options.
`void` | `setSearchBackwards(boolean back)` Set whether to search backwards instead of forwards
`void` | `setStartSet(java.lang.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.
`java.lang.String` | `startSetTipText()` Returns the tip text for this property
`java.lang.String` | `thresholdTipText()` Returns the tip text for this property
`java.lang.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 java.lang.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 java.lang.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 java.lang.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 java.lang.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 java.lang.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 java.lang.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(java.lang.String startSet)
                     throws java.lang.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:
    `java.lang.Exception` - if start set can't be set.

### getStartSet

    public java.lang.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 java.lang.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 java.util.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(java.lang.String[] options)
                    throws java.lang.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:
    `java.lang.Exception` - if an option is not supported

### getOptions

    public java.lang.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 java.lang.String toString()

  returns a description of the search.

  Overrides:
    `toString` in class `java.lang.Object`
  Returns:
    a description of the search as a String.

### search

    public int[] search(ASEvaluation ASEval,
                        Instances data)
                 throws java.lang.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:
    `java.lang.Exception` - if the search can't be completed

### rankedAttributes

    public double[][] rankedAttributes()
                                throws java.lang.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:
    `java.lang.Exception` - if something goes wrong.

### getRevision

    public java.lang.String getRevision()

  Returns the revision string.

  Specified by:
    `getRevision` in interface `RevisionHandler`
  Overrides:
    `getRevision` in class `ASSearch`
  Returns:
    the revision

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