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

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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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<syntaxhighlight lang="mathematica">

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

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

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

</syntaxhighlight>

Line 1,077 ⟶ 1,082:

<syntaxhighlight lang="mathematica">

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

</syntaxhighlight>

Line 1,083 ⟶ 1,088:

<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>

Line 2,082 ⟶ 2,087:

"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>