Comparison of programming languages (associative array): Difference between revisions

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This '''Comparisoncomparison of programming languages (associative arrays)''' compares the features of [[associative array]] [[data structure]]s or array-lookup processing for over 40 computer [[programming language]]s.

==Language support==

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There is no standard implementation of associative arrays in [[C (programming language)|C]], but a 3rd-party library, C Hash Table, with BSD license, is available.<ref>[https://web.archive.org/web/20071015024120/http://www.cl.cam.ac.uk/~cwc22/hashtable/ here], archived [https://web.archive.org/web/20040902160534/http://www.cl.cam.ac.uk/~cwc22/hashtable/ here], with the source code available [https://github.com/davidar/c-hashtable/ here]. [[POSIX]] 1003.1-2001 describes the functions <code>hcreate()</code>, <code>hdestroy()</code> and <code>hsearch()</code></ref>

Another 3rd-party library, uthash, also creates associative arrays from C structures. A structure represents a value, and one of the structure fields serves as the key.<ref>{{cite web |title=uthash: a hash table for C structures |url=httphttps://uthash.sourceforge.net/ |website=Github |access-date=3 August 2020}}</ref>

Finally, the [[GLib]] library also supports associative arrays, along with many other advanced data types and is the recommended implementation of the GNU Project.<ref>{{cite web |title=Hash Tables |url=https://developer.gnome.org/glib/stable/glib-Hash-Tables.html |website=Gnome Developer |access-date=3 August 2020}}</ref>

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Initializing an empty dictionary and adding items in [[Cobra (programming language)|Cobra]]:

{{sxhl|2=python|1=<nowiki/>

dic as Dictionary<of String, String> = Dictionary<of String, String>()

dic.add('Sally Smart', '555-9999')

dic.add('John Doe', '555-1212')

dic.add('J. Random Hacker', '553-1337')

assert dic['Sally Smart'] == '555-9999'

}}

Alternatively, a dictionary can be initialized with all items during construction:

{{sxhl|2=python|1=<nowiki/>

dic = {

'Sally Smart':'555-9999',

'John Doe':'555-1212',

'J. Random Hacker':'553-1337'

}

}}

The dictionary can be enumerated by a for-loop, but there is no guaranteed order:

{{sxhl|2=python|1=<nowiki/>

for key, val in dic

print "[key]'s phone number is [val]"

}}

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===F#===

===={{code|Map<'Key,'Value>}}====

At runtime, [[F Sharp (programming language)|F#]] provides the <code>Collections.Map<'Key,'Value></code> type, which is an immutable [[AVL tree]].

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=====Access by key=====

Values can be looked up via one of the <code>Map</code> members, such as its indexer or <code>Item</code> property (which throw an [[Exception handling|exception]] if the key does not exist) or the <code>TryFind</code> function, which returns an [[option type]] with a value of <{{code>|Some <result></code>|f#}}, for a successful lookup, or <code>None</code>, for an unsuccessful one. [[Pattern matching]] can then be used to extract the raw value from the result, or a default value can be set.

<syntaxhighlight lang="fsharp">

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In both examples above, the <code>sallyNumber</code> value would contain the string <code>"555-9999"</code>.

===={{code|Dictionary<'TKey,'TValue>}}====

Because F# is a .NET language, it also has access to features of the [[.NET Framework]], including the {{code|System.Collections.Generic.Dictionary<'TKey,'TValue>|f#}} type (which is implemented as a [[hash table]]), which is the primary associative array type used in C# and Visual Basic. This type may be preferred when writing code that is intended to operate with other languages on the .NET Framework, or when the performance characteristics of a hash table are preferred over those of an AVL tree.

=====Creation=====

The <code>dict</code> function provides a means of conveniently creating a .NET dictionary that is not intended to be mutated; it accepts a sequence of tuples and returns an immutable object that implements <{{code>|IDictionary<'TKey,'TValue></code>|f#}}.

<syntaxhighlight lang="fsharp">

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Declare dictionary:

<syntaxhighlight lang="julia">

phonebook = Dict( "Sally Smart" => "555-9999", "John Doe" => "555-1212", "J. Random Hacker" => "555-1337" )

</syntaxhighlight>

Access element:

<syntaxhighlight lang="julia">

phonebook["Sally Smart"]

</syntaxhighlight>

Add element:

<syntaxhighlight lang="julia">

phonebook["New Contact"] = "555-2222"

</syntaxhighlight>

Delete element:

<syntaxhighlight lang="julia">

delete!(phonebook, "Sally Smart")

</syntaxhighlight>

Get keys and values as [[Iterator#Implicit iterators|iterables]]:

<syntaxhighlight lang="julia">

keys(phonebook)

values(phonebook)

</syntaxhighlight>

===KornShell 93, and compliant shells===

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Definition:

<syntaxhighlight lang="ksh">

typeset -A phonebook; # ksh93; in bash4+, "typeset" is a synonym of the more preferred "declare", which works identically in this case

phonebook=(["Sally Smart"]="555-9999" ["John Doe"]="555-1212" ["[[J. Random Hacker]]"]="555-1337");

declare -A phonebook; # bash4

phonebook=(["Sally Smart"]="555-9999" ["John Doe"]="555-1212" ["[[J. Random Hacker]]"]="555-1337");

</syntaxhighlight>

Dereference:

<syntaxhighlight lang="ksh">

${phonebook["John Doe"]};

</syntaxhighlight>

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</syntaxhighlight>

Searching for an entry by its key is performed via <code>assoc</code>, which might be configured for the test predicate and direction, especially searching the association list from its end to its front. The result, if positive, returns the entire entry cons, not only its value. Failure to obtain a matching key ledsleads to a return of the <code>NIL</code> value.

<syntaxhighlight lang=Lisp>

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<syntaxhighlight lang="mathematica">

phonebook = <| "Sally Smart" -> "555-9999",

"John Doe" -> "555-1212",

"J. Random Hacker" -> "553-1337" |>;

</syntaxhighlight>

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<syntaxhighlight lang="mathematica">

phonebook[[Key["Sally Smart"]]]

</syntaxhighlight>

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<syntaxhighlight lang="mathematica">

phonebook[["Sally Smart"]]

</syntaxhighlight>

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<syntaxhighlight lang=Java>

String[String] phoneBook = {

"Sally Smart" -> "555-9999",

"John Doe" -> "555-1212",

"J. Random Hacker" -> "553-1337"

};

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// iterate over the values

for (String number : phoneBook) {

System.out.println(number);

}

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// iterate over the keys

for (String name : phoneBook.keys) {

System.out.println(name + " -> " + phoneBook[name]);

}

// phoneBook[name] access a value by a key (it looks like java array access)

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<syntaxhighlight lang=Java>

int[String][][double] a;

java.util.Map<String[Object], Integer> b;

</syntaxhighlight>

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"J. Random Hacker": "555-1337"

}

</syntaxhighlight>

=== TOML ===

[[TOML]] is designed to map directly to a hash map. TOML refers to associative arrays as tables. Tables within TOML can be expressed in either an "unfolded" or an inline approach. Keys can only be strings.<syntaxhighlight lang="toml">[phonebook]

"Sally Smart" = "555-9999"

"John Doe" = "555-1212"

"J. Random Hacker" = "555-1337"</syntaxhighlight><syntaxhighlight lang="toml">

phonebook = { "Sally Smart" = "555-9999", "John Doe" = "555-1212", "J. Random Hacker" = "555-1337" }

</syntaxhighlight>