Multimap: Difference between revisions
unref tag |
|||
| (3 intermediate revisions by 2 users not shown) | |||
| Line 1: | Line 1: | ||
| ⚫ | |||
{{about|the data type|the mathematical concept|Multivalued function|the mapping website|Multimap.com}} |
{{about|the data type|the mathematical concept|Multivalued function|the mapping website|Multimap.com}} |
||
| ⚫ | |||
In [[computer science]], a '''multimap''' (sometimes also '''multihash''', '''multidict''' or '''multidictionary''') is a generalization of a [[associative array|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 [[container (data structure)|container]]s (for example, see [[C++]] [[Standard Template Library]] [[Standard Template Library#Containers|containers]]). Often the multimap is implemented as a map with [[List (computing)|list]]s or [[Set (computer science)|set]]s as the map values. |
In [[computer science]], a '''multimap''' (sometimes also '''multihash''', '''multidict''' or '''multidictionary''') is a generalization of a [[associative array|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 [[container (data structure)|container]]s (for example, see [[C++]] [[Standard Template Library]] [[Standard Template Library#Containers|containers]]). Often the multimap is implemented as a map with [[List (computing)|list]]s or [[Set (computer science)|set]]s as the map values. |
||
| Line 33: | Line 33: | ||
==See also== |
==See also== |
||
* [[Abstract data type]] for the concept of type in general |
|||
* [[Associative array]] for the more fundamental abstract data type |
|||
* [[Multiset]] for the case where same item can appear several times |
* [[Multiset]] for the case where same item can appear several times |
||
Latest revision as of 18:55, 13 May 2024
 | This article needs additional citations for verification. (February 2022) |
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
[edit]- In a student enrollment system, where students may be enrolled in multiple classes simultaneously, there might be an association for each enrollment of a student in a course, where the key is the student ID and the value is the course ID. If a student is enrolled in three courses, there will be three associations containing the same key.
- The index of a book may report any number of references for a given index term, and thus may be coded as a multimap from index terms to any number of reference locations or pages.
- Querystrings may have multiple values associated with a single field. This is commonly generated when a web form allows multiple check boxes or selections to be chosen in response to a single form element.
Language support
[edit]C++
[edit]C++'s Standard Template Library provides the multimap container for the sorted multimap using a self-balancing binary search tree,[1] and SGI's STL extension provides the hash_multimap container, which implements a multimap using a hash table.[2]
As of C++11, the Standard Template Library provides the unordered_multimap for the unordered multimap.[3]
Dart
[edit]Quiver provides a Multimap for Dart.[4]
Java
[edit]Apache Commons Collections provides a MultiMap interface for Java.[5] It also provides a MultiValueMap implementing class that makes a MultiMap out of a Map object and a type of Collection.[6]
Google Guava provides a Multimap interface and implementations of it.[7]
Python
[edit]Python provides a collections.defaultdict class that can be used to create a multimap. The user can instantiate the class as collections.defaultdict(list).
OCaml
[edit]OCaml's standard library module Hashtbl implements a hash table where it's possible to store multiple values for a key.
Scala
[edit]The Scala programming language's API also provides Multimap and implementations.[8]
See also
[edit]- Multiset for the case where same item can appear several times
References
[edit]- ^ "multimap<Key, Data, Compare, Alloc>". Standard Template Library Programmer's Guide. Silicon Graphics International.
- ^ "hash_multimap<Key, HashFcn, EqualKey, Alloc>". Standard Template Library Programmer's Guide. Silicon Graphics International.
- ^ "Working Draft, Standard for Programming Language C++" (PDF). p. 7807.
- ^ "Multimap". Quiver API docs.
- ^ "Interface MultiMap". Commons Collections 3.2.2 API, Apache Commons.
- ^ "Class MultiValueMap". Commons Collections 3.2.2 API, Apache Commons.
- ^ "Interface Multimap<K,V>". Guava Library 2.0. Archived from the original on 2013-01-15. Retrieved 2013-01-01.
- ^ "Scala.collection.mutable.MultiMap". Scala stable API.