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## weka.attributeSelection
Class BestFirst

    java.lang.Object
      weka.attributeSelection.ASSearch
          weka.attributeSelection.BestFirst

All Implemented Interfaces:
  java.io.Serializable, StartSetHandler, OptionHandler

    public class BestFirst

extends ASSearch
implements OptionHandler, StartSetHandler

Class for performing a best first search.

Valid options are:

-P start set
Specify a starting set of attributes. Eg 1,4,7-9.

-D 0 = backward | 1 = forward | 2 = bidirectional
Direction of the search. (default = 1).

-N num
Number of non improving nodes to consider before terminating search. (default = 5).

-S num
Size of lookup cache for evaluated subsets. Expressed as a multiple of the number of attributes in the data set. (default = 1).

Version:
  $Revision: 1.24.2.3 $
Author:
  Mark Hall (mhall@cs.waikato.ac.nz) Martin Guetlein (cashing merit of expanded nodes)
See Also:
  Serialized Form

Nested Class Summary
`class` | `BestFirst.Link2` Class for a node in a linked list.
`class` | `BestFirst.LinkedList2` Class for handling a linked list.

Field Summary
`static Tag[]` | `TAGS_SELECTION`

Constructor Summary
`BestFirst()` Constructor

Method Summary
`java.lang.String` | `directionTipText()` Returns the tip text for this property
`SelectedTag` | `getDirection()` Get the search direction
`int` | `getLookupCacheSize()` Return the maximum size of the evaluated subset cache (expressed as a multiplier for the number of attributes in a data set.
`java.lang.String[]` | `getOptions()` Gets the current settings of BestFirst.
`int` | `getSearchTermination()` Get the termination criterion (number of non-improving nodes).
`java.lang.String` | `getStartSet()` Returns a list of attributes (and or attribute ranges) as a String
`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` | `lookupCacheSizeTipText()` Returns the tip text for this property
`int[]` | `search(ASEvaluation ASEval, Instances data)` Searches the attribute subset space by best first search
`java.lang.String` | `searchTerminationTipText()` Returns the tip text for this property
`void` | `setDirection(SelectedTag d)` Set the search direction
`void` | `setLookupCacheSize(int size)` Set the maximum size of the evaluated subset cache (hashtable).
`void` | `setOptions(java.lang.String[] options)` Parses a given list of options.
`void` | `setSearchTermination(int t)` Set the numnber of non-improving nodes to consider before terminating search.
`void` | `setStartSet(java.lang.String startSet)` Sets a starting set of attributes for the search.
`java.lang.String` | `startSetTipText()` Returns the tip text for this property
`java.lang.String` | `toString()` returns a description of the search as a String

Methods inherited from class weka.attributeSelection.ASSearch
`forName`

Methods inherited from class java.lang.Object
`equals, getClass, hashCode, notify, notifyAll, wait, wait, wait`

Field Detail

### TAGS_SELECTION

    public static final Tag[] TAGS_SELECTION

Constructor Detail

### BestFirst

    public BestFirst()

  Constructor

Method Detail

### globalInfo

    public java.lang.String globalInfo()

  Returns a string describing this search method

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

### 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:

  -P
  Specify a starting set of attributes. Eg 1,4,7-9.

  -D <-1 = backward | 0 = bidirectional | 1 = forward>
  Direction of the search. (default = 1).

  -N
  Number of non improving nodes to consider before terminating search. (default = 5).

  -S
  Size of lookup cache for evaluated subsets. Expressed as a multiple of the number of attributes in the data set. (default = 1).

  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

### setLookupCacheSize

    public void setLookupCacheSize(int size)

  Set the maximum size of the evaluated subset cache (hashtable). This is expressed as a multiplier for the number of attributes in the data set. (default = 1).

  Parameters:
    `size` - the maximum size of the hashtable

### getLookupCacheSize

    public int getLookupCacheSize()

  Return the maximum size of the evaluated subset cache (expressed as a multiplier for the number of attributes in a data set.

  Returns:
    the maximum size of the hashtable.

### lookupCacheSizeTipText

    public java.lang.String lookupCacheSizeTipText()

  Returns the tip text for this property

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

### 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)

### searchTerminationTipText

    public java.lang.String searchTerminationTipText()

  Returns the tip text for this property

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

### setSearchTermination

    public void setSearchTermination(int t)
                              throws java.lang.Exception

  Set the numnber of non-improving nodes to consider before terminating search.

  Parameters:
    `t` - the number of non-improving nodes
  Throws:
    `java.lang.Exception` - if t is less than 1

### getSearchTermination

    public int getSearchTermination()

  Get the termination criterion (number of non-improving nodes).

  Returns:
    the number of non-improving nodes

### directionTipText

    public java.lang.String directionTipText()

  Returns the tip text for this property

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

### setDirection

    public void setDirection(SelectedTag d)

  Set the search direction

  Parameters:
    `d` - the direction of the search

### getDirection

    public SelectedTag getDirection()

  Get the search direction

  Returns:
    the direction of the search

### getOptions

    public java.lang.String[] getOptions()

  Gets the current settings of BestFirst.

  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 as a String

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

### search

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

  Searches the attribute subset space by best first search

  Specified by:
    `search` in class `ASSearch`
  Parameters:
    `ASEvaluator` - 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

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