org.grouplens.lenskit.collections

Class LongUtils

java.lang.Object

org.grouplens.lenskit.collections.LongUtils

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 LongCollection	asLongCollection(Collection<Long> longs) Get a Fastutil LongCollection from a Collection of longs.
static LongSet	asLongSet(Set<Long> longs) Get a Fastutil LongSet from a Set of longs.
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	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

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.

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.

asLongSet

public static LongSet asLongSet(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.

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.

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(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.

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.