org.grouplens.lenskit.data.history

Interface UserHistory<E extends Event>

Type Parameters:

E - The type of event this history contains.

All Superinterfaces:

Collection<E>, Iterable<E>, List<E>

All Known Implementing Classes:

AbstractUserHistory, BasicUserHistory

@ThreadSafe
public interface UserHistory<E extends Event>
extends List<E>

Represents a user profile, associating an immutable list of events with a user. The events are in timestamp order. Histories also can memoize summaries and other computed properties of themselves.

Compatibility

Public

Method Summary

Modifier and Type	Method and Description
<T extends Event> UserHistory<T>	filter(Class<T> type) Filter the user history to only contain elements of a particular type.
UserHistory<E>	filter(Predicate<? super E> pred) Filter the user history with a predicate.
long	getUserId() Retrieve the user ID.
LongSet	itemSet() Get the set of items touched by events in this history.
<T> T	memoize(Function<? super UserHistory<E>,? extends T> func) Apply a function to this history, memoizing its return value.

Methods inherited from interface java.util.List

add, add, addAll, addAll, clear, contains, containsAll, equals, get, hashCode, indexOf, isEmpty, iterator, lastIndexOf, listIterator, listIterator, remove, remove, removeAll, replaceAll, retainAll, set, size, sort, spliterator, subList, toArray, toArray

Methods inherited from interface java.util.Collection

parallelStream, removeIf, stream

Methods inherited from interface java.lang.Iterable

forEach

Method Detail

getUserId

long getUserId()

Retrieve the user ID.

Returns:

The ID of the user who owns this history.

filter

<T extends Event> UserHistory<T> filter(Class<T> type)

Filter the user history to only contain elements of a particular type.

Type Parameters:

T - The type of element to include.

Parameters:

type - The type of elements to include.

Returns:

A user history containing only the elements of the specified type.

filter

UserHistory<E> filter(Predicate<? super E> pred)

Filter the user history with a predicate.

Parameters:

pred - The predicate to with which to filter the history.

Returns:

A copy of this user history containing only elements which match the predicate.

itemSet

LongSet itemSet()

Get the set of items touched by events in this history. Only nonnegative item IDs are considered.

Returns:

The set of all item IDs used in events in this history.

memoize

<T> T memoize(Function<? super UserHistory<E>,? extends T> func)

Apply a function to this history, memoizing its return value. Used for caching things like summaries. The function should appropriately define its Function.equals(Object) and Object.hashCode() methods in order for memoization to work well.

This method is not guaranteed to be synchronized. It is safe to memoize distinct functions in parallel, but potentially-parallel use of the same function must be synchronized by client code or the function may be called twice. The implementation in AbstractUserHistory uses a ConcurrentHashMap. Multiple calls are therefore safe, but may result in extra work. All implementations must maintain this safety guarantee, although they may do so by synchronizing this method.

Type Parameters:

T - The return type of the function.

Parameters:

func - The function to call and memoize.

Returns:

The return value of func.