org.apache.mahout.cf.taste.impl.recommender.slopeone.file
Class FileDiffStorage

java.lang.Object
  org.apache.mahout.cf.taste.impl.recommender.slopeone.file.FileDiffStorage

All Implemented Interfaces:

Refreshable, DiffStorage

public final class FileDiffStorage
extends Object
implements DiffStorage

DiffStorage which reads pre-computed diffs from a file and stores in memory. The file should have one diff per line:

itemID1,itemID2,diff[,count[,mk,sk]]

The fourth column is optional, and is a count representing the number of occurrences of the item-item pair that contribute to the diff. It is assumed to be 1 if not present. The fifth and sixth arguments are computed values used by FullRunningAverageAndStdDev implementations to compute a running standard deviation. They are required if using Weighting.WEIGHTED with SlopeOneRecommender.

Commas or tabs can be delimiters. This is intended for use in conjuction with the output of SlopeOneAverageDiffsJob.

Note that the same item-item pair should not appear on multiple lines -- one line per item-item pair.

Constructor Summary

FileDiffStorage(File dataFile, long maxEntries)

Method Summary

void	addItemPref(long userID, long itemIDA, float prefValue) Updates internal data structures to reflect a new preference value for an item.
RunningAverage	getAverageItemPref(long itemID)
RunningAverage	getDiff(long itemID1, long itemID2)
RunningAverage[]	getDiffs(long userID, long itemID, PreferenceArray prefs)
FastIDSet	getRecommendableItemIDs(long userID)
void	refresh(Collection<Refreshable> alreadyRefreshed) Triggers "refresh" -- whatever that means -- of the implementation.
void	removeItemPref(long userID, long itemIDA, float prefValue) Updates internal data structures to reflect an update in a preference value for an item.
void	updateItemPref(long itemID, float prefDelta) Updates internal data structures to reflect an update in a preference value for an item.

Methods inherited from class java.lang.Object

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

Constructor Detail

FileDiffStorage

public FileDiffStorage(File dataFile,
                       long maxEntries)
                throws FileNotFoundException

Parameters:

dataFile - diffs file

maxEntries - maximum number of diffs to store

Throws:

FileNotFoundException - if data file does not exist or is a directory

Method Detail

getDiff

public RunningAverage getDiff(long itemID1,
                              long itemID2)

Specified by:

getDiff in interface DiffStorage

Returns:

RunningAverage encapsulating the average difference in preferences between items corresponding to itemID1 and itemID2, in that direction; that is, it's the average of item 2's preferences minus item 1's preferences

getDiffs

public RunningAverage[] getDiffs(long userID,
                                 long itemID,
                                 PreferenceArray prefs)

Specified by:

getDiffs in interface DiffStorage

Parameters:

userID - user ID to get diffs for

itemID - itemID to assess

prefs - user's preferendces

Returns:

RunningAverages for that user's item-item diffs

getAverageItemPref

public RunningAverage getAverageItemPref(long itemID)

Specified by:

getAverageItemPref in interface DiffStorage

Returns:

RunningAverage encapsulating the average preference for the given item

addItemPref

public void addItemPref(long userID,
                        long itemIDA,
                        float prefValue)

Description copied from interface: DiffStorage

Updates internal data structures to reflect a new preference value for an item.

Specified by:

addItemPref in interface DiffStorage

Parameters:

userID - user whose pref is being added

itemIDA - item to add preference value for

prefValue - new preference value

updateItemPref

public void updateItemPref(long itemID,
                           float prefDelta)

Description copied from interface: DiffStorage

Updates internal data structures to reflect an update in a preference value for an item.

Specified by:

updateItemPref in interface DiffStorage

Parameters:

itemID - item to update preference value for

prefDelta - amount by which preference value changed

removeItemPref

public void removeItemPref(long userID,
                           long itemIDA,
                           float prefValue)

Description copied from interface: DiffStorage

Updates internal data structures to reflect an update in a preference value for an item.

Specified by:

removeItemPref in interface DiffStorage

Parameters:

userID - user whose pref is being removed

itemIDA - item to update preference value for

prefValue - old preference value

getRecommendableItemIDs

public FastIDSet getRecommendableItemIDs(long userID)

Specified by:

getRecommendableItemIDs in interface DiffStorage

Returns:

item IDs that may possibly be recommended to the given user, which may not be all items since the item-item diff matrix may be sparse

refresh

public void refresh(Collection<Refreshable> alreadyRefreshed)

Description copied from interface: Refreshable

Triggers "refresh" -- whatever that means -- of the implementation. The general contract is that any should always leave itself in a consistent, operational state, and that the refresh atomically updates internal state from old to new.

Specified by:

refresh in interface Refreshable

Parameters:

alreadyRefreshed - s that are known to have already been refreshed as a result of an initial call to a method on some object. This ensure that objects in a refresh dependency graph aren't refreshed twice needlessly.