org.lenskit.util.collections

Class LongUtils

java.lang.Object

org.lenskit.util.collections.LongUtils

@ParametersAreNonnullByDefault
public final class LongUtils
extends Object

Utilities for working with longs and collections of them from Fastutil.

Since:

2.0

Compatibility

Public

Method Summary

Modifier and Type	Method and Description
static Long2DoubleFunction	asLong2DoubleFunction(Map<Long,Double> map) Create a long-to-double function from a map, casting if appropriate.
static LongCollection	asLongCollection(Collection<Long> longs) Get a Fastutil LongCollection from a Collection of longs.
static LongList	asLongList(List<Long> longs)
static LongSet	asLongSet(Collection<Long> longs) Get a Fastutil LongSet from a Collection of longs.
static LongSet	asLongSet(Set<Long> longs) Get a Fastutil LongSet from a Set of longs.
static Long2DoubleMap	constantDoubleMap(Set<Long> keys, double value) Create a map that maps a group of items to the same value.
static Long2DoubleSortedMap	frozenMap(Map<Long,Double> map) Create a frozen long-to-double map.
static LongSortedSet	frozenSet(Collection<Long> longs) Create a frozen long set.
static boolean	hasNCommonItems(LongSortedSet a, LongSortedSet b, int n) Check if two sets have at least a given number of common items.
static int	intersectSize(LongSortedSet a, LongSortedSet b) Compute the size of the intersection of two sets.
static Long2IntMap	itemRanks(LongList results) Compute the ranks for a list of longs.
static LongComparator	keyValueComparator(Long2DoubleFunction vals) Create a comparator that compares long keys by associated double values.
static LongSortedSet	packedSet(Collection<Long> longs) Pack longs into a sorted set.
static LongSortedSet	packedSet(long... longs) Pack longs into a sorted set.
static LongSortedSet	randomSubset(LongSet set, int num, LongSet exclude, Random rng) Selects a random subset of n longs from a given set of longs such that no selected items is in a second set of longs.
static LongSet	randomSubset(LongSet set, int num, Random random) Selects a random subset of n longs from a given set of longs.
static LongSortedSet	setDifference(LongSet items, LongSet exclude) Compute the set difference of two sets.
static LongSortedSet	setIntersect(LongSet a, LongSet b) Compute the intersection of two sets.
static LongSortedSet	setIntersect(LongSortedSet a, LongSortedSet b) Compute the intersection of two sets.
static LongSortedSet	setUnion(LongSet a, LongSet b) Compute the union of two sets.
static LongSortedSet	setUnion(LongSortedSet a, LongSortedSet b) Compute the union of two sets.
static int	unionSize(LongSortedSet a, LongSortedSet b) Compute the size of the union of two sets.

Methods inherited from class java.lang.Object

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

Method Detail

frozenMap

public static Long2DoubleSortedMap frozenMap(Map<Long,Double> map)

Create a frozen long-to-double map. This effectively creates a copy of a map, but if the provided map is an instance of Long2DoubleSortedArrayMap, which is immutable, it is returned as-is for efficiency.

Parameters:

map - The source map.

Returns:

An immutable map with the same data as map.

frozenSet

public static LongSortedSet frozenSet(Collection<Long> longs)

Create a frozen long set. If the underlying collection is already an immutable sorted set (specifically, a LongSortedArraySet, it is used as-is. Otherwise, it is copied into a sorted array set.

This is equivalent to packedSet(Collection).

Parameters:

longs - The collection.

Returns:

The sorted array set.

See Also:

packedSet(Collection)

packedSet

public static LongSortedSet packedSet(Collection<Long> longs)

Pack longs into a sorted set.

Parameters:

longs - A collection of longs.

Returns:

An efficient sorted set containing the numbers in longs.

packedSet

public static LongSortedSet packedSet(long... longs)

Pack longs into a sorted set.

Parameters:

longs - An array of longs. This array is copied, not wrapped.

Returns:

An efficient sorted set containing the numbers in longs.

keyValueComparator

public static LongComparator keyValueComparator(Long2DoubleFunction vals)

Create a comparator that compares long keys by associated double values.

Parameters:

vals - The value map.

Returns:

A comparator that will compare keys by looking them up in a map.

asLongCollection

public static LongCollection asLongCollection(Collection<Long> longs)

Get a Fastutil LongCollection from a Collection of longs. This method simply casts the collection, if possible, and returns a wrapper otherwise.

Parameters:

longs - A collection of longs.

Returns:

The collection as a LongCollection.

asLong2DoubleFunction

public static Long2DoubleFunction asLong2DoubleFunction(Map<Long,Double> map)

Create a long-to-double function from a map, casting if appropriate. Useful to allow unboxed access to maps that are really fastutil maps.

Parameters:

map - The map.

Returns:

A function backed by map, or map if it is a Fastutil map.

asLongList

public static LongList asLongList(List<Long> longs)

constantDoubleMap

public static Long2DoubleMap constantDoubleMap(Set<Long> keys,
                                               double value)

Create a map that maps a group of items to the same value.

Parameters:

keys - The keys.

value - The value.

Returns:

A map that contains all keys, mapping each of them to value.

asLongSet

public static LongSet asLongSet(@Nullable
                                Set<Long> longs)

Get a Fastutil LongSet from a Set of longs.

Parameters:

longs - The set of longs.

Returns:

longs as a fastutil LongSet. If longs is already a LongSet, it is cast.

asLongSet

public static LongSet asLongSet(@Nullable
                                Collection<Long> longs)

Get a Fastutil LongSet from a Collection of longs.

Parameters:

longs - The set of longs.

Returns:

longs as a fastutil LongSet. If longs is already a LongSet, it is cast.

itemRanks

public static Long2IntMap itemRanks(LongList results)

Compute the ranks for a list of longs.

Parameters:

results - The list of longs.

Returns:

The map of ranks; its default return value will be -1.

setDifference

public static LongSortedSet setDifference(LongSet items,
                                          LongSet exclude)

Compute the set difference of two sets.

Parameters:

items - The initial set

exclude - The items to remove

Returns:

The elements of items that are not in exclude.

intersectSize

public static int intersectSize(LongSortedSet a,
                                LongSortedSet b)

Compute the size of the intersection of two sets.

Parameters:

a - The first set.

b - The second set.

Returns:

The size of the intersection of the two sets.

hasNCommonItems

public static boolean hasNCommonItems(LongSortedSet a,
                                      LongSortedSet b,
                                      int n)

Check if two sets have at least a given number of common items.

Parameters:

a - The first set.

b - The second set.

n - The number of common items to require.

Returns:

true if the two sets have at least n common items.

unionSize

public static int unionSize(LongSortedSet a,
                            LongSortedSet b)

Compute the size of the union of two sets.

Parameters:

a - The first set.

b - The second set.

Returns:

The size of the union of the two sets.

setUnion

public static LongSortedSet setUnion(LongSet a,
                                     LongSet b)

Compute the union of two sets.

Parameters:

a - The first set.

b - The second set.

Returns:

The elements of items that are not in exclude.

setUnion

public static LongSortedSet setUnion(LongSortedSet a,
                                     LongSortedSet b)

Compute the union of two sets.

Parameters:

a - The first set.

b - The second set.

Returns:

The elements of items that are not in exclude.

setIntersect

public static LongSortedSet setIntersect(LongSet a,
                                         LongSet b)

Compute the intersection of two sets.

Parameters:

a - The first set.

b - The second set.

Returns:

The elements present in both sets.

setIntersect

public static LongSortedSet setIntersect(LongSortedSet a,
                                         LongSortedSet b)

Compute the intersection of two sets.

Parameters:

a - The first set.

b - The second set.

Returns:

The elements present in both sets.

randomSubset

public static LongSet randomSubset(LongSet set,
                                   int num,
                                   Random random)

Selects a random subset of n longs from a given set of longs. If fewer than n items can be selected the whole set is returned.

Parameters:

set - the set of items to select from

num - The number of random items to add.

random - a random number generator to be used.

Returns:

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

randomSubset

public static LongSortedSet randomSubset(LongSet set,
                                         int num,
                                         LongSet exclude,
                                         Random rng)

Selects a random subset of n longs from a given set of longs such that no selected items is in a second set of longs. If fewer than n items can be selected the whole set is returned.

Parameters:

set - the set of items to select from

num - The number of random items to add.

exclude - a set of longs which must not be returned

rng - a random number generator to be used.

Returns:

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