org.grouplens.lenskit.eval.metrics.topn

Class ItemSelectors

java.lang.Object

org.grouplens.lenskit.eval.metrics.topn.ItemSelectors

public final class ItemSelectors
extends Object

Class providing various item selectors.

Method Summary

Modifier and Type	Method and Description
static ItemSelector	addNRandom(ItemSelector base, int nRandom) Select items selected by a selector, plus additional randomly-selected items.
static ItemSelector	allItems() Item selector that selects all items.
static ItemSelector	allItemsExcept(ItemSelector base)
static ItemSelector	fixed(Collection<Long> items) Select a fixed collection of items.
static ItemSelector	fixed(long... items) Select a fixed collection of items.
static ItemSelector	mostPopular(int n) Select the most popular items.
static ItemSelector	nRandom(int n) Randomly selects items from the universe.
static ItemSelector	randomSubset(ItemSelector base, int n) Randomly select items selected by another selector.
static ItemSelector	setDifference(ItemSelector selectorToKeep, ItemSelector selectorToNotKeep) Selects the set difference between two other selectors
static ItemSelector	testItems() Item selector that selects test items.
static ItemSelector	testRatingMatches(org.hamcrest.Matcher<Double> matcher) Select items where the user's test rating matches a condition.
static ItemSelector	trainingItems() Item selector that selects training items.
static ItemSelector	union(ItemSelector selectorOne, ItemSelector selectorTwo) selects any items selected by at least one of two other selectors.

Methods inherited from class java.lang.Object

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

Method Detail

allItems

public static ItemSelector allItems()

Item selector that selects all items.

Returns:

An item selector that selects the universe of items.

testItems

public static ItemSelector testItems()

Item selector that selects test items.

Returns:

An item selector that selects the items from the user's test set.

trainingItems

public static ItemSelector trainingItems()

Item selector that selects training items.

Returns:

An item selector that selects the items from the user's training set.

testRatingMatches

public static ItemSelector testRatingMatches(org.hamcrest.Matcher<Double> matcher)

Select items where the user's test rating matches a condition. For example, using the matcher Matchers.greaterThanOrEqualTo(Comparable) will select items that the user has rated at least a particular value.

Parameters:

matcher - The matcher for test ratings.

Returns:

An item selector that selects items with matching test ratings.

allItemsExcept

public static ItemSelector allItemsExcept(ItemSelector base)

addNRandom

public static ItemSelector addNRandom(ItemSelector base,
                                      int nRandom)

Select items selected by a selector, plus additional randomly-selected items.

Parameters:

base - The base selector (e.g. testItems()).

nRandom - The number of random items to add.

Returns:

An item selector that selects the items selected by base plus an additional nRandom items.

randomSubset

public static ItemSelector randomSubset(ItemSelector base,
                                        int n)

Randomly select items selected by another selector.

Parameters:

base - The base selector (e.g. allItems()).

n - The number of random items to select.

Returns:

An item selector that selects n items from the items selected by base, or simply the items selected by base if there are fewer then n items selected.

nRandom

public static ItemSelector nRandom(int n)

Randomly selects items from the universe. Short for ItemSelectors.randomSubset(ItemSelectors.allItems, n)

mostPopular

public static ItemSelector mostPopular(int n)

Select the most popular items.

Parameters:

n - The number of items to select.

Returns:

A selector factory that will select the n items with the most events.

setDifference

public static ItemSelector setDifference(ItemSelector selectorToKeep,
                                         ItemSelector selectorToNotKeep)

Selects the set difference between two other selectors

Parameters:

selectorToKeep - selects items that are to be kept

selectorToNotKeep - selects items that are to be excluded

Returns:

an item selector which selects every item that is selected by selectorToKeep and not selected by selectorToNotKeep.

union

public static ItemSelector union(ItemSelector selectorOne,
                                 ItemSelector selectorTwo)

selects any items selected by at least one of two other selectors.

fixed

public static ItemSelector fixed(Collection<Long> items)

Select a fixed collection of items.

Parameters:

items - The set of items. to select.

Returns:

A selector that selects items.

fixed

public static ItemSelector fixed(long... items)

Select a fixed collection of items.

Parameters:

items - The items to select.

Returns:

A selector that selects items.