In computer science, a multimap (sometimes also multihash or multidict) 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.
Python provides a
collections.defaultdict class that can be used to create a multimap. The user can instantiate the class as
OCaml's standard library module
Hashtbl implements a hash table where it's possible to store multiple values for a key.