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public interface IDMigrator
Mahout 0.2 changed the framework to operate only in terms of numeric (long) ID values for users and items.
This is, obviously, not compatible with applications that used other key types -- most commonly
String
. Implementation of this class provide support for mapping String to longs and vice versa in
order to provide a smoother migration path to applications that must still use strings as IDs.
The mapping from strings to 64-bit numeric values is fixed here, to provide a standard implementation that
is 'portable' or reproducible outside the framework easily. See toLongID(String)
.
Because this mapping is deterministically computable, it does not need to be stored. Indeed, subclasses' job is to store the reverse mapping. There are an infinite number of strings but only a fixed number of longs, so, it is possible for two strings to map to the same value. Subclasses do not treat this as an error but rather retain only the most recent mapping, overwriting a previous mapping. The probability of collision in a 64-bit space is quite small, but not zero. However, in the context of a collaborative filtering problem, the consequence of a collision is small, at worst -- perhaps one user receives another recommendations.
Method Summary | |
---|---|
void |
initialize(java.lang.Iterable<java.lang.String> stringIDs)
Make the mapping aware of the given string IDs. |
void |
storeMapping(long longID,
java.lang.String stringID)
Stores the reverse long-to-String mapping in some kind of backing store. |
long |
toLongID(java.lang.String stringID)
|
java.lang.String |
toStringID(long longID)
|
Method Detail |
---|
long toLongID(java.lang.String stringID)
String
's UTF-8 encoding as a
long.
TasteException
- if an error occurs while storing the mappingjava.lang.String toStringID(long longID) throws TasteException
TasteException
- if an error occurs while retrieving the mappingvoid storeMapping(long longID, java.lang.String stringID) throws TasteException
initialize(Iterable)
) for every String that might be encountered
in the application, or else the mapping will not be known.
longID
- long IDstringID
- string ID that maps to/from that long ID
TasteException
- if an error occurs while saving the mappingvoid initialize(java.lang.Iterable<java.lang.String> stringIDs) throws TasteException
TasteException
- if an error occurs while storing the mappings
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