This Comparison of programming languages (associative arrays) compares the features of associative array data structures or array-lookup processing for over 40 computer programming languages.
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C# uses the collection classes provided by the .NET Framework. The most commonly used associative array type is `System.Collections.Generic.Dictionary`, which is implemented as a mutable hash table.
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Hash tables are commonly used to implement many types of in-memory tables. They are used to implement associative arrays (arrays whose indices are arbitrary strings or other complicated objects), especially in interpreted programming languages like Ruby, Python, and PHP. When storing a new item into a multimap and a hash collision occurs, the multimap unconditionally stores both items. When storing a new item into a typical associative array and a hash collision occurs, but the actual keys themselves are different, the associative array likewise stores both items.
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A hash array mapped trie (HAMT) is an implementation of an associative array that combines the characteristics of a hash table and an array mapped trie. It is a refined version of the more general notion of a hash tree.
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However, if the key of the new item exactly matches the key of an old item, the associative array typically erases the old item and overwrites it with the new item, so every item in the table has a unique key.
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In February 2009, Bash 4.0 introduced support for associative arrays. Associative array indices are strings, in a manner similar to AWK or Tcl. They can be used to emulate multidimensional arrays. Bash 4 also switches its license to GPLv3; some users suspect this licensing change is why MacOS continues to use older versions.
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Reverse lookup is a procedure of using a value to retrieve a unique key in an associative array.. Applications of reverse lookup include reverse DNS lookup, which provides the domain name associated with a particular IP address,. and a reverse telephone directory, which provides the name of the entity associated with a particular telephone number..
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In an associative array (or map, dictionary, lookup table), like in a dictionary, a lookup on a key (like a word) provides a value (like a definition). The value might be a reference to a compound data structure. A hash table is usually an efficient implementation, and thus this data type is often known as a "hash".
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In Ruby, symbols can be created with a literal form, or by converting a string. They can be used as an identifier or an interned string. Two symbols with the same contents will always refer to the same object. It is considered a best practice to use symbols as keys to an associative array in Ruby.
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So, these languages usually allow arbitrary new elements to be created at any time. This choice precludes the implementation of array types as array data structures. That is, those languages use array-like syntax to implement a more general associative array semantics, and must therefore be implemented by a hash table or some other search data structure.
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Instead, use a Boolean data type tag array to operate the recursive function to release the memory. The extra memory space required is close to 2n+(n)bits. Contains a two-dimensional array of dynamically allocated memory and a Boolean data type tag array. Stack, queue, associative array, and tree structure can be implemented as buckets.
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The system uses a client–server architecture. The servers maintain a key–value associative array; the clients populate this array and query it by key. Keys are up to 250 bytes long and values can be at most 1 megabyte in size. Clients use client- side libraries to contact the servers which, by default, expose their service at port 11211.
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The super column consists of a (unique) super column name, and a number of columns. A super column is a tuple (a pair) with a binary super column name and a value that maps it to many columns. They consist of a key–value pairs, where the values are columns. Theoretically speaking, super columns are (sorted) associative array of columns.
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However the execution complexity can still be maintained as an efficient sorting method of O(n + k). Array of dynamically allocated memory can be implemented by linked list, stack, queue, associative array, tree structure, etc. An array object such as JavaScript is applicable. The difference in data structure is related to the speed of data access and thus the time required for sorting.
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PHP's built-in array type is, in reality, an associative array. Even when using numerical indexes, PHP internally stores arrays as associative arrays.About the implementation of Arrays in PHP So, PHP can have non-consecutively numerically-indexed arrays. The keys have to be of integer (floating point numbers are truncated to integer) or string type, while values can be of arbitrary types, including other arrays and objects.
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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.
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Perl 5 has built-in, language-level support for associative arrays. Modern Perl refers to associative arrays as hashes; the term associative array is found in older documentation but is considered somewhat archaic. Perl 5 hashes are flat: keys are strings and values are scalars. However, values may be references to arrays or other hashes, and the standard Perl 5 module Tie::RefHash enables hashes to be used with reference keys.
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The function that does this value-for-function-object replacement can generically wrap any referentially transparent function. Consider the following pseudocode (where it is assumed that functions are first-class values): function memoized-call (F is a function object parameter) if F has no attached array values then allocate an associative array called values; attach values to F; end if; if F.values[arguments] is empty then F.values[arguments] = F(arguments); end if; return F.values[arguments]; end function In order to call an automatically memoized version of `factorial` using the above strategy, rather than calling `factorial` directly, code invokes `memoized- call(factorial(n))`. Each such call first checks to see if a holder array has been allocated to store results, and if not, attaches that array. If no entry exists at the position `values[arguments]` (where `arguments` are used as the key of the associative array), a real call is made to `factorial` with the supplied arguments.
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The object table is an associative array of indexes to graphical object structures defined within the metafile. WMF and EMF files handle object processing differently to EMF+ records in EMF files. As a WMF and EMF file is being processed, the records are read into an object table once an object is defined. If an object is deleted then the object is released from the table and the identifier can be reused.
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The tables can have multiple dimensions, of fixed or variable lengths and are usually portable between computer platforms, requiring only a change to the interpreter, not the algorithm itself - the logic of which is essentially embodied within the table structure and content. The structure of the table may be similar to a multimap associative array, where a data value (or combination of data values) may be mapped to one or more functions to be performed.
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In machine learning, feature hashing, also known as the hashing trick (by analogy to the kernel trick), is a fast and space-efficient way of vectorizing features, i.e. turning arbitrary features into indices in a vector or matrix. It works by applying a hash function to the features and using their hash values as indices directly, rather than looking the indices up in an associative array. This trick is often attributed to Weinberger et al.
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If an implementation supports ±∞, then this value may be computed as +∞ (`inf`), however. An element of an array is undefined when its index is out of bounds, as is the value in an associative array for a key which it does not contain. An argument of a variadic function which was not passed to it, is undefined within the function body. A variable which is not initialized has undefined (or unpredictable) value until it is assigned.
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Suppose that the set of loans made by a library is represented in a data structure. Each book in a library may be checked out only by a single library patron at a time. However, a single patron may be able to check out multiple books. Therefore, the information about which books are checked out to which patrons may be represented by an associative array, in which the books are the keys and the patrons are the values.
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The program can create a complete text representation of any group of objects by calling these methods, which are almost always already implemented in the base associative array class."Archives and Serializations Programming Guide", Apple Inc., 2012 For programs that use very large data sets, this sort of individual file storage is not appropriate, and a database management system (DB) is required. Some DB systems natively store associative arrays by serializing the data and then storing that serialized data and the key.
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Perl programmers may initialize a hash (or associative array) from a list of key/value pairs. If the keys are separated from the values with the `=>` operator (sometimes called a fat comma), rather than a comma, they may be unquoted (barewords ). The following lines are equivalent: %favorite = ('joe', "red", 'sam', "blue"); %favorite = (joe => 'red', sam => 'blue'); Individual values in a hash are accessed by providing the corresponding key, in curly braces. The `$` sigil identifies the accessed element as a scalar.
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It has to then be copied with `idup` to obtain a string to be used for the associative array values (the `idup` property of arrays returns an immutable duplicate of the array, which is required since the `dstring` type is actually `immutable(dchar)[]`). Built-in associative arrays require immutable keys. # The `~=` operator appends a new dstring to the values of the associate dynamic array. # `toLower`, `join` and `chomp` are string functions that D allows the use of with a method syntax.
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Collections are first and foremost abstractions that are useful in formulating solutions to computing problems. Viewed in this light, they retain important links to underlying mathematical concepts which can be lost when the focus is on the implementation. For example, a priority queue is often implemented as a heap, while an associative array is often implemented as a hash table, so these abstract types are often referred to by this preferred implementation, as a "heap" or a "hash", though this is not strictly correct.
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Key–value (KV) stores use the associative array (also called a map or dictionary) as their fundamental data model. In this model, data is represented as a collection of key–value pairs, such that each possible key appears at most once in the collection. The key–value model is one of the simplest non-trivial data models, and richer data models are often implemented as an extension of it. The key–value model can be extended to a discretely ordered model that maintains keys in lexicographic order.
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The idea of an associative array that allows data to be accessed by its value rather than by its address dates back to the mid-1940s in the work of Konrad Zuse and Vannevar Bush,. but hash tables were not described until 1953, in an IBM memorandum by Hans Peter Luhn. Luhn used a different collision resolution method, chaining, rather than linear probing.. summarizes the early history of linear probing. It was the first open addressing method, and was originally synonymous with open addressing.
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In computer science, a U-form is an abstract data type comprising a collection of attribute-value pairs associated with a universally-unique identifier (UUID). A U-form essentially comprises an associative array augmented with a UUID and with keys limited to strings. The UUID that is associated with a u-form is immutable, however all data "contained" in the u-form are mutable (including the keys/names). The mutability of contained data combined with an immutable identifier make implementations of fully mutable, replicable digital objects possible.
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Notably an object will not be used until it is specifically selected during record playback. This differs for EMF+ files, which also use an associative array via a hashmap which records the object along with an object identifier. However, unlike WMF and EMF files which can delete an object, when a new object is created that has the same index as an existing object, the entry in the table is replaced with the new object. An EMF file also does not need to specifically select an object before it is used.
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Rlab borrows some of the best features of the MATLAB language but provides them through a different syntax that has been modified in order to be more expressive while reducing ambiguity. The variable scoping rules facilitate the creation of larger programs and re-usable program libraries. A heterogeneous associative array datatype has been added to allow users to create and operate on arbitrary data structures. The fundamental data type is the dense floating point matrix (either real or complex), though string and sparse numerical matrices (both real and complex) are also provided.
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Prototypal inheritance in JavaScript is described by Douglas Crockford as: In JavaScript, an object is an associative array, augmented with a prototype (see below); each string key provides the name for an object property, and there are two syntactical ways to specify such a name: dot notation (`obj.x = 10`) and bracket notation (`obj['x'] = 10`). A property may be added, rebound, or deleted at run-time. Most properties of an object (and any property that belongs to an object's prototype inheritance chain) can be enumerated using a `for...in` loop.
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The arrays are heterogeneous: a single array can have keys of different types. PHP's associative arrays can be used to represent trees, lists, stacks, queues, and other common data structures not built into PHP. An associative array can be declared using the following syntax: $phonebook = array(); $phonebook['Sally Smart'] = '555-9999'; $phonebook['John Doe'] = '555-1212'; $phonebook['J. Random Hacker'] = '555-1337'; // or $phonebook = array( 'Sally Smart' => '555-9999', 'John Doe' => '555-1212', 'J. Random Hacker' => '555-1337', ); // or, as of PHP 5.4 $phonebook = [ 'Sally Smart' => '555-9999', 'John Doe' => '555-1212', 'J.
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Dictionary of Algorithms and Data Structures The advantage of search trees is that their efficient search time given the tree is reasonably balanced, which is to say the leaves at either end are of comparable depths. Various search-tree data structures exist, several of which also allow efficient insertion and deletion of elements, which operations then have to maintain tree balance. Search trees are often used to implement an associative array. The search tree algorithm uses the key from the key-value pair to find a location, and then the application stores the entire key–value pair at that particular location.
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In computer programming and particularly in Lisp, an association list, often referred to as an alist, is a linked list in which each list element (or node) comprises a key and a value. The association list is said to associate the value with the key. In order to find the value associated with a given key, a sequential search is used: each element of the list is searched in turn, starting at the head, until the key is found. Associative lists provide a simple way of implementing an associative array, but are efficient only when the number of keys is very small.
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The disadvantage of association lists is that the time to search is , where is the length of the list. For large lists, this may be much slower than the times that can be obtained by representing an associative array as a binary search tree or as a hash table. Additionally, unless the list is regularly pruned to remove elements with duplicate keys, multiple values associated with the same key will increase the size of the list, and thus the time to search, without providing any compensatory advantage. One advantage of association lists is that a new element can be added in constant time.
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As a result, the base language is light—the full reference interpreter is only about 247 kB compiled—and easily adaptable to a broad range of applications. Lua is a dynamically typed language intended for use as an extension or scripting language and is compact enough to fit on a variety of host platforms. It supports only a small number of atomic data structures such as boolean values, numbers (double-precision floating point and 64-bit integers by default), and strings. Typical data structures such as arrays, sets, lists, and records can be represented using Lua's single native data structure, the table, which is essentially a heterogeneous associative array.
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This graph compares the average number of CPU cache misses required to look up elements in large hash tables (far exceeding size of the cache) with chaining and linear probing. Linear probing performs better due to better locality of reference, though as the table gets full, its performance degrades drastically. The most frequently used general purpose implementation of an associative array is with a hash table: an array combined with a hash function that separates each key into a separate "bucket" of the array. The basic idea behind a hash table is that accessing an element of an array via its index is a simple, constant-time operation.
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The term array is often used to mean array data type, a kind of data type provided by most high-level programming languages that consists of a collection of values or variables that can be selected by one or more indices computed at run-time. Array types are often implemented by array structures; however, in some languages they may be implemented by hash tables, linked lists, search trees, or other data structures. The term is also used, especially in the description of algorithms, to mean associative array or "abstract array", a theoretical computer science model (an abstract data type or ADT) intended to capture the essential properties of arrays.
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In computer science, a fusion tree is a type of tree data structure that implements an associative array on -bit integers. When operating on a collection of key–value pairs, it uses space and performs searches in time, which is asymptotically faster than a traditional self-balancing binary search tree, and also better than the van Emde Boas tree for large values of . It achieves this speed by exploiting certain constant-time operations that can be done on a machine word. Fusion trees were invented in 1990 by Michael Fredman and Dan Willard.. Several advances have been made since Fredman and Willard's original 1990 paper.
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A trie for keys "A", "to", "tea", "ted", "ten", "i", "in", and "inn". Note that this example does not have all the children alphabetically sorted from left to right as it should be (the root and node 't'). In computer science, a trie, also called digital tree or prefix tree, is a kind of search tree—an ordered tree data structure used to store a dynamic set or associative array where the keys are usually strings. Unlike a binary search tree, no node in the tree stores the key associated with that node; instead, its position in the tree defines the key with which it is associated; i.e.
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An object is similar to a map—both let you set keys to values, retrieve those values, delete keys, and detect whether a value is stored at a key. For this reason (and because there were no built-in alternatives), objects historically have been used as maps. However, there are important differences that make a map preferable in certain cases. In JavaScript an object is a mapping from property names to values—that is, an associative array with one caveat: the keys of an object must be either a string or a symbol (native objects and primitives implicitly converted to a string keys are allowed).
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Random Hacker' => '555-1337', ]; // or $phonebook['contacts']['Sally Smart']['number'] = '555-9999'; $phonebook['contacts']['John Doe']['number'] = '555-1212'; $phonebook['contacts']['J. Random Hacker']['number'] = '555-1337'; PHP can loop through an associative array as follows: foreach ($phonebook as $name => $number) { echo 'Number for ', $name, ': ', $number, " "; } // For the last array example it is used like this foreach ($phonebook['contacts'] as $name => $num) { echo 'Name: ', $name, ', number: ', $num['number'], " "; } PHP has an extensive set of functions to operate on arrays. Associative arrays that can use objects as keys, instead of strings and integers, can be implemented with the `SplObjectStorage` class from the Standard PHP Library (SPL).
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Finally, the entry in the array at the key position is returned to the caller. The above strategy requires explicit wrapping at each call to a function that is to be memoized. In those languages that allow closures, memoization can be effected implicitly by a functor factory that returns a wrapped memoized function object. In pseudocode, this can be expressed as follows: function construct-memoized-functor (F is a function object parameter) allocate a function object called memoized-version; let memoized-version(arguments) be if self has no attached array values then [self is a reference to this object] allocate an associative array called values; attach values to self; end if; if self.
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The term polymorphism refers to the ability of code (especially, functions or classes) to act on values of multiple types, or to the ability of different instances of the same data structure to contain elements of different types. Type systems that allow polymorphism generally do so in order to improve the potential for code re-use: in a language with polymorphism, programmers need only implement a data structure such as a list or an associative array once, rather than once for each type of element with which they plan to use it. For this reason computer scientists sometimes call the use of certain forms of polymorphism generic programming. The type-theoretic foundations of polymorphism are closely related to those of abstraction, modularity and (in some cases) subtyping.
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A small phone book as a hash table In computing, a hash table (hash map) is a data structure that implements an associative array abstract data type, a structure that can map keys to values. A hash table uses a hash function to compute an index, also called a hash code, into an array of buckets or slots, from which the desired value can be found. During lookup, the key is hashed and the resulting hash indicates where the corresponding value is stored. Ideally, the hash function will assign each key to a unique bucket, but most hash table designs employ an imperfect hash function, which might cause hash collisions where the hash function generates the same index for more than one key.
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Associative arrays may also be stored in unbalanced binary search trees or in data structures specialized to a particular type of keys such as radix trees, tries, Judy arrays, or van Emde Boas trees, though the ability of these implementation methods within comparison to hash tables varies; for instance, Judy trees remain indicated to perform with a smaller quantity of efficiency than hash tables, while carefully selected hash tables generally perform with increased efficiency in comparison to adaptive radix trees, with potentially greater restrictions on the types of data that they can handle. The advantages of these alternative structures come from their ability to handle operations beyond the basic ones of an associative array, such as finding the mapping whose key is the closest to a queried key, when the query is not itself present in the set of mappings.
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An associative array is an abstract data type that can be used to maintain a collection of key–value pairs and look up the value associated with a given key. The association list provides a simple way of implementing this data type. To test whether a key is associated with a value in a given association list, search the list starting at its first node and continuing either until a node containing the key has been found or until the search reaches the end of the list (in which case the key is not present). To add a new key–value pair to an association list, create a new node for that key-value pair, set the node's link to be the previous first element of the association list, and replace the first element of the association list with the new node.
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In languages such as Lua, more sophisticated techniques exist which allow a function to be replaced by a new function with the same name, which would permit: factorial = construct-memoized- functor(factorial) Essentially, such techniques involve attaching the original function object to the created functor and forwarding calls to the original function being memoized via an alias when a call to the actual function is required (to avoid endless recursion), as illustrated below: function construct-memoized-functor (F is a function object parameter) allocate a function object called memoized-version; let memoized-version(arguments) be if self has no attached array values then [self is a reference to this object] allocate an associative array called values; attach values to self; allocate a new function object called alias; attach alias to self; [for later ability to invoke F indirectly] self.alias = F; end if; if self.values[arguments] is empty then self.values[arguments] = self.
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