In computer science, a multimap (sometimes also multihash, multidict or multidictionary) 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.

Examples

Language support

C++

C++'s Standard Template Library provides the container for the sorted multimap using a self-balancing binary search tree, and SGI's STL extension provides the container, which implements a multimap using a hash table. As of C++11, the Standard Template Library provides the for the unordered multimap.

Dart

Quiver provides a Multimap for Dart.

Java

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 a Multimap interface and implementations of it.

Python

Python provides a class that can be used to create a multimap. The user can instantiate the class as.

OCaml

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

Scala

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