weka.associations

Class ItemSet

java.lang.Object

weka.associations.ItemSet

All Implemented Interfaces:

Serializable, RevisionHandler

Direct Known Subclasses:

AprioriItemSet, LabeledItemSet

public class ItemSet
extends Object
implements Serializable, RevisionHandler

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. The class provides the general methods used for item sets in class - and standard association rule mining.

Version:

$Revision: 8034 $

Author:

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

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
ItemSet(int totalTrans) Constructor
ItemSet(int[] array) Contsructor
ItemSet(int totalTrans, int[] array) Constructor

Method Summary

Methods

Modifier and Type	Method and Description
boolean	containedBy(Instance instance) Checks if an instance contains an item set.
int	counter() Gets the counter
static FastVector	deleteItemSets(FastVector itemSets, int minSupport, int maxSupport) Deletes all item sets that don't have minimum support.
boolean	equals(Object itemSet) Tests if two item sets are equal.
static Hashtable	getHashtable(FastVector itemSets, int initialSize) Return a hashtable filled with the given item sets.
String	getRevision() Returns the revision string.
boolean	getTreatZeroAsMissing() Gets whether zeros (i.e.
int	hashCode() Produces a hash code for a item set.
int	itemAt(int k) Gest the index of the value of the specified attribute
int[]	items() Gest the item set as an int array
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, 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.
void	setCounter(int count) Sets the counter
void	setItem(int[] items) Sets an item sets
void	setItemAt(int value, int k) Sets the index of an attribute value
void	setTreatZeroAsMissing(boolean z) Sets whether zeros (i.e.
static FastVector	singletons(Instances instances) Converts the header info of the given set of instances into a set of item sets (singletons).
int	support() Outputs the support for an item set.
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

getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ItemSet

public ItemSet(int totalTrans)

Constructor

Parameters:

totalTrans - the total number of transactions in the data

ItemSet

public ItemSet(int totalTrans,
       int[] array)

Constructor

Parameters:

totalTrans - the total number of transactions in the data

array - the attribute values encoded in an int array

ItemSet

public ItemSet(int[] array)

Contsructor

Parameters:

array - the item set represented as an int array

Method Detail

containedBy

public 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:

maxSupport - the maximum support

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 boolean equals(Object itemSet)

Tests if two item sets are equal.

Overrides:

equals in class Object

Parameters:

itemSet - another item set

Returns:

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

getHashtable

public static 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 int hashCode()

Produces a hash code for a item set.

Overrides:

hashCode in class 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:

totalTrans - thetotal number of transactions

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,
                       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 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:

Exception - if singletons can't be generated successfully

support

public int support()

Outputs the support for an item set.

Returns:

the support

toString

public 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 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

counter

public int counter()

Gets the counter

Returns:

the counter

items

public int[] items()

Gest the item set as an int array

Returns:

int array represneting an item set

itemAt

public int itemAt(int k)

Gest the index of the value of the specified attribute

Parameters:

k - the attribute index

Returns:

the index of the attribute value

setCounter

public void setCounter(int count)

Sets the counter

Parameters:

count - the counter

setItem

public void setItem(int[] items)

Sets an item sets

Parameters:

items - an int array representing an item set

setItemAt

public void setItemAt(int value,
             int k)

Sets the index of an attribute value

Parameters:

value - the inex of the attribute value

k - the index of the attribute

setTreatZeroAsMissing

public void setTreatZeroAsMissing(boolean z)

Sets whether zeros (i.e. the first value of a nominal attribute) should be treated as missing values.

Parameters:

z - true if zeros should be treated as missing values.

getTreatZeroAsMissing

public boolean getTreatZeroAsMissing()

Gets whether zeros (i.e. the first value of a nominal attribute) is to be treated int he same way as missing values.

Returns:

true if zeros are to be treated like missing values.

getRevision

public String getRevision()

Returns the revision string.

Specified by:

getRevision in interface RevisionHandler

Returns:

the revision