com.twitter.common.collections

Class Multimaps

java.lang.Object

com.twitter.common.collections.Multimaps

public final class Multimaps
extends Object

Utility class for functions related to Multimaps in the java collections library.

Method Summary

Modifier and Type	Method and Description
static <K> Set<K>	getLargeGroups(com.google.common.collect.Multimap<K,?> map, int minSize) Returns the set of keys associated with groups of a size greater than or equal to a given size.
static <K> Set<K>	getLargestGroups(com.google.common.collect.Multimap<K,?> map, int topValues) Returns the set of keys associated with the largest values in the multimap.
static <K,V> com.google.common.collect.Multimap<K,V>	prune(com.google.common.collect.Multimap<K,V> map, int minSize) Convenience method to prune key/values pairs where the size of the value collection is below a threshold.
static <K,V> com.google.common.collect.Multimap<K,V>	prune(com.google.common.collect.Multimap<K,V> map, com.google.common.base.Predicate<Collection<V>> filterRule) Prunes a multimap based on a predicate, returning the pruned values.

Methods inherited from class java.lang.Object

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

Method Detail

prune

public static <K,V> com.google.common.collect.Multimap<K,V> prune(com.google.common.collect.Multimap<K,V> map,
                                                                  com.google.common.base.Predicate<Collection<V>> filterRule)

Prunes a multimap based on a predicate, returning the pruned values. The input map will be modified.

Type Parameters:

K - The key type in the multimap.

V - The value type in the multimap.

Parameters:

map - The multimap to prune.

filterRule - The pruning rule. When the predicate returns false for an entry, it will be pruned, otherwise it will be retained.

Returns:

A new multimap, containing the pruned keys/values.

prune

public static <K,V> com.google.common.collect.Multimap<K,V> prune(com.google.common.collect.Multimap<K,V> map,
                                                                  int minSize)

Convenience method to prune key/values pairs where the size of the value collection is below a threshold.

Type Parameters:

K - The key type in the multimap.

V - The value type in the multimap.

Parameters:

map - The multimap to prune.

minSize - The minimum size for retained value collections.

Returns:

A new multimap, containing the pruned keys/values.

getLargeGroups

public static <K> Set<K> getLargeGroups(com.google.common.collect.Multimap<K,?> map,
                                        int minSize)

Returns the set of keys associated with groups of a size greater than or equal to a given size.

Type Parameters:

K - The key type for the multimap.

Parameters:

map - The multimap to search.

minSize - The minimum size to return associated keys for.

Returns:

The keys associated with groups of size greater than or equal to minSize.

getLargestGroups

public static <K> Set<K> getLargestGroups(com.google.common.collect.Multimap<K,?> map,
                                          int topValues)

Returns the set of keys associated with the largest values in the multimap.

Parameters:

map - The multimap to search.

topValues - Number of groupings to find the keys for.

Returns:

The keys associated with the largest groups, of maximum size topValues.