LBJ2.learn
Class Lexicon.PruningPolicy

java.lang.Object
  LBJ2.learn.Lexicon.PruningPolicy

Enclosing class:

Lexicon

public static class Lexicon.PruningPolicy
extends java.lang.Object

Represents the feature counting policy of a lexicon. Objects of this type are used to identify and describe a desired pruning policy. In particular, the description of a pruning policy includes feature count thresholds which sometimes need to be computed in terms of data. Space is allocated within objects of this type for storing these thresholds whenever they are computed.

The three pruning policies are described below.

None

No pruning is performed.

Absolute

Features whose counts within a given dataset fall below an absolute threshold are pruned from that dataset.

Percentage

Features whose counts within a given dataset are lower than a given percentage of the most common feature's count are pruned from that dataset.

Field Summary

static int	ABSOLUTE Represents pruning with an absolute threshold.
private int	index Can be used to index the names array.
private static java.lang.String[]	names The names of the different counting policies as strings.
static int	NONE Represents no pruning.
private double	percentage The percentage associated with the "Percentage" policy described above.
static int	PERCENTAGE Represents pruning with a percentage threshold.
private int[]	thresholds Feature count thresholds which may either be specified by the policy explicitly or computed in terms of data.

Constructor Summary

Lexicon.PruningPolicy()
Creates a new pruning policy in which no features will be pruned.

Lexicon.PruningPolicy(double p)
Creates a new "Percentage" policy with the given percentage.

Lexicon.PruningPolicy(int t)
Creates a new "Absolute" policy with the given threshold.

Method Summary

double	getPercentage() Returns the value of percentage.
int	getThreshold(int i) Returns the value of the ith threshold in thresholds when in "Percentage" mode, but ignores the parameter i and returns the first element of thresholds when in "Absolute" mode.
boolean	isAbsolute() true iff the policy is absolute thresholding.
boolean	isNone() true iff the policy is no pruning.
boolean	isPercentage() true iff the policy is percentage thresholding.
void	setThresholds(int[] t) Use this method to establish feature count thresholds in the "Percentage" policy.
java.lang.String	toString() Retrieves the name of the policy represented by this object.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

NONE

public static final int NONE

Represents no pruning.

See Also:

Constant Field Values

ABSOLUTE

public static final int ABSOLUTE

Represents pruning with an absolute threshold.

See Also:

Constant Field Values

PERCENTAGE

public static final int PERCENTAGE

Represents pruning with a percentage threshold.

See Also:

Constant Field Values

names

private static final java.lang.String[] names

The names of the different counting policies as strings.

index

private int index

Can be used to index the names array.

percentage

private double percentage

The percentage associated with the "Percentage" policy described above.

thresholds

private int[] thresholds

Feature count thresholds which may either be specified by the policy explicitly or computed in terms of data.

Constructor Detail

Lexicon.PruningPolicy

public Lexicon.PruningPolicy()

Creates a new pruning policy in which no features will be pruned.

Lexicon.PruningPolicy

public Lexicon.PruningPolicy(double p)

Creates a new "Percentage" policy with the given percentage.

Parameters:

p - The percentage.

Lexicon.PruningPolicy

public Lexicon.PruningPolicy(int t)

Creates a new "Absolute" policy with the given threshold.

Parameters:

t - The threshold.

Method Detail

isNone

public boolean isNone()

true iff the policy is no pruning.

isAbsolute

public boolean isAbsolute()

true iff the policy is absolute thresholding.

isPercentage

public boolean isPercentage()

true iff the policy is percentage thresholding.

setThresholds

public void setThresholds(int[] t)

Use this method to establish feature count thresholds in the "Percentage" policy.

Parameters:

t - The new feature count thresholds.

getThreshold

public int getThreshold(int i)

Returns the value of the i^th threshold in thresholds when in "Percentage" mode, but ignores the parameter i and returns the first element of thresholds when in "Absolute" mode.

Parameters:

i - An index.

Returns:

A feature count threshold.

getPercentage

public double getPercentage()

Returns the value of percentage.

toString

public java.lang.String toString()

Retrieves the name of the policy represented by this object.

Overrides:

toString in class java.lang.Object