public class FileItemSimilarity extends Object implements ItemSimilarity
An ItemSimilarity
backed by a comma-delimited file. This class typically expects a file where each line
contains an item ID, followed by another item ID, followed by a similarity value, separated by commas. You may also
use tabs.
The similarity value is assumed to be parseable as a double
having a value between -1 and 1. The
item IDs are parsed as long
s. Similarities are symmetric so for a pair of items you do not have to
include 2 lines in the file.
This class will reload data from the data file when refresh(Collection)
is called, unless the file
has been reloaded very recently already.
This class is not intended for use with very large amounts of data. For that, a JDBC-backed ItemSimilarity
and a database are more appropriate.
Modifier and Type | Field and Description |
---|---|
static long |
DEFAULT_MIN_RELOAD_INTERVAL_MS |
Constructor and Description |
---|
FileItemSimilarity(File dataFile) |
FileItemSimilarity(File dataFile,
long minReloadIntervalMS) |
Modifier and Type | Method and Description |
---|---|
long[] |
allSimilarItemIDs(long itemID) |
double[] |
itemSimilarities(long itemID1,
long[] itemID2s)
A bulk-get version of
ItemSimilarity.itemSimilarity(long, long) . |
double |
itemSimilarity(long itemID1,
long itemID2)
Returns the degree of similarity, of two items, based on the preferences that users have expressed for
the items.
|
void |
refresh(Collection<Refreshable> alreadyRefreshed)
Triggers "refresh" -- whatever that means -- of the implementation.
|
protected void |
reload() |
String |
toString() |
public static final long DEFAULT_MIN_RELOAD_INTERVAL_MS
public FileItemSimilarity(File dataFile)
dataFile
- file containing the similarity datapublic FileItemSimilarity(File dataFile, long minReloadIntervalMS)
minReloadIntervalMS
- the minimum interval in milliseconds after which a full reload of the original datafile is done
when refresh() is calledFileItemSimilarity(File)
public double[] itemSimilarities(long itemID1, long[] itemID2s) throws TasteException
ItemSimilarity
A bulk-get version of ItemSimilarity.itemSimilarity(long, long)
.
itemSimilarities
in interface ItemSimilarity
itemID1
- first item IDitemID2s
- second item IDs to compute similarity withNoSuchItemException
- if any item is known to be non-existent in the dataTasteException
- if an error occurs while accessing the datapublic long[] allSimilarItemIDs(long itemID) throws TasteException
allSimilarItemIDs
in interface ItemSimilarity
TasteException
public double itemSimilarity(long itemID1, long itemID2) throws TasteException
ItemSimilarity
Returns the degree of similarity, of two items, based on the preferences that users have expressed for the items.
itemSimilarity
in interface ItemSimilarity
itemID1
- first item IDitemID2
- second item IDDouble.NaN
similarity is unknownNoSuchItemException
- if either item is known to be non-existent in the dataTasteException
- if an error occurs while accessing the datapublic void refresh(Collection<Refreshable> alreadyRefreshed)
Refreshable
Triggers "refresh" -- whatever that means -- of the implementation. The general contract is that any
Refreshable
should always leave itself in a consistent, operational state, and that the refresh
atomically updates internal state from old to new.
refresh
in interface Refreshable
alreadyRefreshed
- Refreshable
s that are known to have already been
refreshed as a result of an initial call to a {#refresh(Collection)} method on some
object. This ensure that objects in a refresh dependency graph aren't refreshed twice
needlessly.protected void reload()
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