Multimap (data structure)

In computer science, a multimap (sometimes also multihash) is a generalization of a map or associative array abstract data type in which more than one value may be associated with and returned for a given key. Both map and multimap are particular cases of containers (for example, see C++ Standard Template Library containers). Often the multimap is implemented as a map with lists or sets as the map values.

C++'s Standard Template Library provides the multimap container for the sorted multimap using a self-balancing binary search tree, and SGI's STL extension provides the hash_multimap container, which implements a multimap using a hash table.

Quiver provides a Multimap for Dart.

Apache Commons Collections provides a MultiMap interface for Java. It also provides a MultiValueMap implementing class that makes a MultiMap out of a Map object and a type of Collection.

Google Guava provides an interface Multimap and implementations.

OCaml's standard library module Hashtbl implements a hash table where it's possible to store multiple values for a key.

The Scala programming language's API also provides Multimap and implementations

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