weka.associations
Class ItemSet

java.lang.Object
  |
  +--weka.associations.ItemSet

All Implemented Interfaces:

java.io.Serializable

public class ItemSet

extends java.lang.Object

implements java.io.Serializable

Class for storing a set of items. Item sets are stored in a lexicographic order, which is determined by the header information of the set of instances used for generating the set of items. All methods in this class assume that item sets are stored in lexicographic order.

Author:

Eibe Frank (eibe@cs.waikato.ac.nz)

See Also:

Serialized Form

Field Summary

protected int	m_counter Counter for how many transactions contain this item set.
protected int[]	m_items The items stored as an array of of ints.
protected int	m_totalTransactions The total number of transactions

Constructor Summary

ItemSet(int totalTrans)
Constructor

Method Summary

static double	confidenceForRule(ItemSet premise, ItemSet consequence) Outputs the confidence for a rule.
boolean	containedBy(Instance instance) Checks if an instance contains an item set.
double	convictionForRule(ItemSet premise, ItemSet consequence, int premiseCount, int consequenceCount) Outputs the conviction for a rule.
static FastVector	deleteItemSets(FastVector itemSets, int minSupport, int maxSupport) Deletes all item sets that don't have minimum support.
boolean	equals(java.lang.Object itemSet) Tests if two item sets are equal.
FastVector[]	generateRules(double minConfidence, FastVector hashtables, int numItemsInSet) Generates all rules for an item set.
FastVector[]	generateRulesBruteForce(double minMetric, int metricType, FastVector hashtables, int numItemsInSet, int numTransactions, double significanceLevel) Generates all significant rules for an item set.
static java.util.Hashtable	getHashtable(FastVector itemSets, int initialSize) Return a hashtable filled with the given item sets.
int	hashCode() Produces a hash code for a item set.
double	leverageForRule(ItemSet premise, ItemSet consequence, int premiseCount, int consequenceCount) Outputs the leverage for a rule.
double	liftForRule(ItemSet premise, ItemSet consequence, int consequenceCount) Outputs the lift for a rule.
static FastVector	mergeAllItemSets(FastVector itemSets, int size, int totalTrans) Merges all item sets in the set of (k-1)-item sets to create the (k)-item sets and updates the counters.
static FastVector	pruneItemSets(FastVector toPrune, java.util.Hashtable kMinusOne) Prunes a set of (k)-item sets using the given (k-1)-item sets.
static void	pruneRules(FastVector[] rules, double minConfidence) Prunes a set of rules.
static FastVector	singletons(Instances instances) Converts the header info of the given set of instances into a set of item sets (singletons).
ItemSet	subtract(ItemSet toSubtract) Subtracts an item set from another one.
int	support() Outputs the support for an item set.
java.lang.String	toString(Instances instances) Returns the contents of an item set as a string.
void	upDateCounter(Instance instance) Updates counter of item set with respect to given transaction.
static void	upDateCounters(FastVector itemSets, Instances instances) Updates counters for a set of item sets and a set of instances.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Field Detail

m_items

protected int[] m_items

The items stored as an array of of ints.

m_counter

protected int m_counter

Counter for how many transactions contain this item set.

m_totalTransactions

protected int m_totalTransactions

The total number of transactions

Constructor Detail

ItemSet

public ItemSet(int totalTrans)

Constructor

Parameters:

totalTrans - the total number of transactions in the data

Method Detail

confidenceForRule

public static double confidenceForRule(ItemSet premise,
                                       ItemSet consequence)

Outputs the confidence for a rule.

Parameters:

premise - the premise of the rule

consequence - the consequence of the rule

Returns:

the confidence on the training data

liftForRule

public double liftForRule(ItemSet premise,
                          ItemSet consequence,
                          int consequenceCount)

Outputs the lift for a rule. Lift is defined as:
confidence / prob(consequence)

Parameters:

premise - the premise of the rule

consequence - the consequence of the rule

consequenceCount - how many times the consequence occurs independent of the premise

Returns:

the lift on the training data

leverageForRule

public double leverageForRule(ItemSet premise,
                              ItemSet consequence,
                              int premiseCount,
                              int consequenceCount)

Outputs the leverage for a rule. Leverage is defined as:
prob(premise & consequence) - (prob(premise) * prob(consequence))

Parameters:

premise - the premise of the rule

consequence - the consequence of the rule

premiseCount - how many times the premise occurs independent of the consequent

consequenceCount - how many times the consequence occurs independent of the premise

Returns:

the leverage on the training data

convictionForRule

public double convictionForRule(ItemSet premise,
                                ItemSet consequence,
                                int premiseCount,
                                int consequenceCount)

Outputs the conviction for a rule. Conviction is defined as:
prob(premise) * prob(!consequence) / prob(premise & !consequence)

Parameters:

premise - the premise of the rule

consequence - the consequence of the rule

premiseCount - how many times the premise occurs independent of the consequent

consequenceCount - how many times the consequence occurs independent of the premise

Returns:

the conviction on the training data

containedBy

public final boolean containedBy(Instance instance)

Checks if an instance contains an item set.

Parameters:

instance - the instance to be tested

Returns:

true if the given instance contains this item set

deleteItemSets

public static FastVector deleteItemSets(FastVector itemSets,
                                        int minSupport,
                                        int maxSupport)

Deletes all item sets that don't have minimum support.

Parameters:

itemSets - the set of item sets to be pruned

minSupport - the minimum number of transactions to be covered

Returns:

the reduced set of item sets

equals

public final boolean equals(java.lang.Object itemSet)

Tests if two item sets are equal.

Overrides:

equals in class java.lang.Object

Parameters:

itemSet - another item set

Returns:

true if this item set contains the same items as the given one

generateRules

public final FastVector[] generateRules(double minConfidence,
                                        FastVector hashtables,
                                        int numItemsInSet)

Generates all rules for an item set.

Parameters:

minConfidence - the minimum confidence the rules have to have

hashtables - containing all(!) previously generated item sets

numItemsInSet - the size of the item set for which the rules are to be generated

Returns:

all the rules with minimum confidence for the given item set

generateRulesBruteForce

public final FastVector[] generateRulesBruteForce(double minMetric,
                                                  int metricType,
                                                  FastVector hashtables,
                                                  int numItemsInSet,
                                                  int numTransactions,
                                                  double significanceLevel)
                                           throws java.lang.Exception

Generates all significant rules for an item set.

Parameters:

minMetric - the minimum metric (confidence, lift, leverage, improvement) the rules have to have

metricType - (confidence=0, lift, leverage, improvement)

hashtables - containing all(!) previously generated item sets

numItemsInSet - the size of the item set for which the rules are to be generated

the - significance level for testing the rules

Returns:

all the rules with minimum metric for the given item set

Throws:

java.lang.Exception - if something goes wrong

getHashtable

public static java.util.Hashtable getHashtable(FastVector itemSets,
                                               int initialSize)

Return a hashtable filled with the given item sets.

Parameters:

itemSets - the set of item sets to be used for filling the hash table

initialSize - the initial size of the hashtable

Returns:

the generated hashtable

hashCode

public final int hashCode()

Produces a hash code for a item set.

Overrides:

hashCode in class java.lang.Object

Returns:

a hash code for a set of items

mergeAllItemSets

public static FastVector mergeAllItemSets(FastVector itemSets,
                                          int size,
                                          int totalTrans)

Merges all item sets in the set of (k-1)-item sets to create the (k)-item sets and updates the counters.

Parameters:

itemSets - the set of (k-1)-item sets

size - the value of (k-1)

Returns:

the generated (k)-item sets

pruneItemSets

public static FastVector pruneItemSets(FastVector toPrune,
                                       java.util.Hashtable kMinusOne)

Prunes a set of (k)-item sets using the given (k-1)-item sets.

Parameters:

toPrune - the set of (k)-item sets to be pruned

kMinusOne - the (k-1)-item sets to be used for pruning

Returns:

the pruned set of item sets

pruneRules

public static void pruneRules(FastVector[] rules,
                              double minConfidence)

Prunes a set of rules.

Parameters:

rules - a two-dimensional array of lists of item sets. The first list of item sets contains the premises, the second one the consequences.

minConfidence - the minimum confidence the rules have to have

singletons

public static FastVector singletons(Instances instances)
                             throws java.lang.Exception

Converts the header info of the given set of instances into a set of item sets (singletons). The ordering of values in the header file determines the lexicographic order.

Parameters:

instances - the set of instances whose header info is to be used

Returns:

a set of item sets, each containing a single item

Throws:

java.lang.Exception - if singletons can't be generated successfully

subtract

public final ItemSet subtract(ItemSet toSubtract)

Subtracts an item set from another one.

Parameters:

toSubtract - the item set to be subtracted from this one.

Returns:

an item set that only contains items form this item sets that are not contained by toSubtract

support

public final int support()

Outputs the support for an item set.

Returns:

the support

toString

public final java.lang.String toString(Instances instances)

Returns the contents of an item set as a string.

Parameters:

instances - contains the relevant header information

Returns:

string describing the item set

upDateCounter

public final void upDateCounter(Instance instance)

Updates counter of item set with respect to given transaction.

Parameters:

instance - the instance to be used for ubdating the counter

upDateCounters

public static void upDateCounters(FastVector itemSets,
                                  Instances instances)

Updates counters for a set of item sets and a set of instances.

Parameters:

itemSets - the set of item sets which are to be updated

instances - the instances to be used for updating the counters