org.grouplens.lenskit.indexes

Class IdIndexMapping

java.lang.Object

org.grouplens.lenskit.indexes.IdIndexMapping

All Implemented Interfaces:

Serializable

Direct Known Subclasses:

MutableIdIndexMapping

public abstract class IdIndexMapping
extends Object
implements Serializable

Bidirectional mapping between long IDs and consecutive, 0-based integer indexes. This makes it easier to store information about sparse IDs (e.g. user or item IDs) in dense, indexed data structures such as arrays, matrices, or lists.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
IdIndexMapping()

Method Summary

Modifier and Type	Method and Description
boolean	containsId(long id) Query whether this index contains a particular ID.
static IdIndexMapping	create(Collection<? extends Long> ids)
abstract long	getId(int idx) Get the ID for an index.
abstract LongList	getIdList() Get the list of indexed IDs.
int	getIndex(long id) Get the index of an ID.
abstract int	size() Get the size of this index.
abstract int	tryGetIndex(long id) Try to get the index for an ID, returning a negative value if it does not exist.

Methods inherited from class java.lang.Object

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

Constructor Detail

IdIndexMapping

public IdIndexMapping()

Method Detail

getIndex

public int getIndex(long id)

Get the index of an ID.

Parameters:

id - The ID to query.

Returns:

The ID's index or a negative value if the ID does not exist.

Throws:

IllegalArgumentException - if the ID is not in the index.

containsId

public boolean containsId(long id)

Query whether this index contains a particular ID.

Parameters:

id - The ID to look for.

Returns:

true if the index contains the ID.

tryGetIndex

public abstract int tryGetIndex(long id)

Try to get the index for an ID, returning a negative value if it does not exist. This method is like getIndex(long), except it returns a negative value instead of throwing an exception if the id does not exist.

Parameters:

id - The ID to look for.

Returns:

The index of the ID, or a negative value if it is not in the index.

getId

public abstract long getId(int idx)

Get the ID for an index.

Parameters:

idx - The index of the ID to retrieve.

Returns:

The ID for the given idx.

Throws:

IndexOutOfBoundsException - if idx is not a valid index.

size

public abstract int size()

Get the size of this index.

Returns:

The number of indexed IDs.

getIdList

public abstract LongList getIdList()

Get the list of indexed IDs.

Returns:

The list of IDs in the index. No ID will appear twice.

create

public static IdIndexMapping create(Collection<? extends Long> ids)