Associative array/Iteration

Show how to iterate over the key-value pairs of an associative array, and print each pair out. Also show how to iterate just over the keys, or the values, if there is a separate way to do that in your language.

See also

Array
Associative array: Creation, Iteration
Collections
Compound data type
Doubly-linked list: Definition, Element definition, Element insertion, List Traversal, Element Removal
Linked list
Queue: Definition, Usage
Set
Singly-linked list: Element definition, Element insertion, List Traversal, Element Removal
Stack

Ada

<lang Ada>with Ada.Text_IO; use Ada.Text_IO; with Ada.Containers.Indefinite_Ordered_Maps;

procedure Test_Iteration is

  package String_Maps is
     new Ada.Containers.Indefinite_Ordered_Maps (String, Integer);
  use String_Maps;
  A     : Map;
  Index : Cursor;

begin

  A.Insert ("hello", 1);
  A.Insert ("world", 2);
  A.Insert ("!",     3);
  Index := A.First;
  while Index /= No_Element loop
     Put_Line (Key (Index) & Integer'Image (Element (Index)));
     Index := Next (Index);
  end loop;

end Test_Iteration;</lang>

Output:

! 3
hello 1
world 2

Aime

<lang aime>record r; text s;

r_put(r, "A", 33); # an integer value r_put(r, "C", 2.5); # a real value r_put(r, "B", "associative"); # a string value

if (r_first(r, s)) {

   do {
       o_form("key ~, value ~ (~)\n", s, r[s], r_type(r, s));
   } while (r_greater(r, s, s));

}</lang>

Output:

key A, value 33 (integer)
key B, value associative (text)
key C, value 2.5 (real)

App Inventor

Associative arrays in App Inventor are lists of key:value 'pairs'.
When a list is organized as pairs, the lookup in pairs block can be used to retrieve an associated value from a key name.
<VIEW BLOCKS AND ANDROID APP>

AutoHotkey

Works with: AutoHotkey_L

From the documentation<lang AutoHotkey>; Create an associative array obj := Object("red", 0xFF0000, "blue", 0x0000FF, "green", 0x00FF00) enum := obj._NewEnum() While enum[key, value]

   t .= key "=" value "`n"

MsgBox % t</lang>

AWK

In AWK "arrays" are always associative arrays, and the only way to iterate over them is by keys (indexes in the AWK terminology)

<lang awk>BEGIN {

 a["hello"] = 1
 a["world"] = 2
 a["!"] = 3

 # iterate over keys
 for(key in a) {
   print key, a[key]
 }

}</lang>

Babel

Use the entsha (mnemonic: "get entries from the hash") operator to obtain a list of all entries, where each entry consists of a 3-element list containing the hashed-key, the key and the value in that order.

<lang babel>((main

   { (('foo'   12)
      ('bar'   33)
      ('baz'   42)) 
   mkhash !

   entsha
   dup
   {1 ith nl <<} each

   "-----\n" <<

   {2 ith %d nl <<} each})

(mkhash

   { <- newha ->
   { <- dup ->
       dup 1 ith
       <- 0 ith ->
       inskha }
   each }))</lang>

This program generates the following

Output:

foo
baz
bar
-----
12
42
33

Note that the entsha operator does not return the entries of the hash in any particular order. In general, there is no automatic way to recover the order in which the entries were inserted into the hash.

BASIC256

Solution is at Associative_array/Creation#BASIC256.

BBC BASIC

<lang bbcbasic> REM Store some values with their keys:

     PROCputdict(mydict$, "FF0000", "red")
     PROCputdict(mydict$, "00FF00", "green")
     PROCputdict(mydict$, "0000FF", "blue")
     
     REM Iterate through the dictionary:
     i% = 1
     REPEAT
       i% = FNdict(mydict$, i%, v$, k$)
       PRINT v$, k$
     UNTIL i% = 0
     END
     
     DEF PROCputdict(RETURN dict$, value$, key$)
     IF dict$ = "" dict$ = CHR$(0)
     dict$ += key$ + CHR$(1) + value$ + CHR$(0)
     ENDPROC
     
     DEF FNdict(dict$, I%, RETURN value$, RETURN key$)
     LOCAL J%, K%
     J% = INSTR(dict$, CHR$(1), I%)
     K% = INSTR(dict$, CHR$(0), J%)
     value$ = MID$(dict$, I%+1, J%-I%-1)
     key$ = MID$(dict$, J%+1, K%-J%-1)
     IF K% >= LEN(dict$) THEN K% = 0
     = K%</lang>

Bracmat

<lang bracmat>( new$hash:?myhash & (myhash..insert)$(title."Some title") & (myhash..insert)$(formula.a+b+x^7) & (myhash..insert)$(fruit.apples oranges kiwis) & (myhash..insert)$(meat.) & (myhash..insert)$(fruit.melons bananas) & (myhash..remove)$formula & (myhash..insert)$(formula.x^2+y^2) & (myhash..forall)

 $ ( 
   =   key value
     .     whl
         ' ( !arg:(?key.?value) ?arg
           & put$("key:" !key "\nvalue:" !value \n)
           )
       & put$\n
   )

);</lang>

Output:

key: meat
value:

key: title
value: Some title

key: formula
value: x^2+y^2

key: fruit
value: melons bananas
key: fruit
value: apples oranges kiwis

Brat

<lang brat>h = [ hello: 1 world: 2 :! : 3]

Iterate over key, value pairs

h.each { k, v |

 p "Key: #{k} Value: #{v}"

}

Iterate over keys

h.each_key { k |

 p "Key: #{k}"

}

Iterate over values

h.each_value { v |

 p "Value: #{v}"

}</lang>

C

Solution is at Associative arrays/Creation/C.

C++

Works with: C++11

<lang cpp>#include <iostream>

include <map>
include <string>

int main() {

 std::map<std::string, int> dict {
   {"One", 1},
   {"Two", 2},
   {"Three", 7}
 };

 dict["Three"] = 3;

 std::cout << "One: " << dict["One"] << std::endl;
 std::cout << "Key/Value pairs: " << std::endl;
 for(auto& kv: dict) {
   std::cout << "  " << kv.first << ": " << kv.second << std::endl;
 }

 return 0;

}</lang>

Pre C++11: <lang cpp>std::map<std::string, int> myDict; myDict["hello"] = 1; myDict["world"] = 2; myDict["!"] = 3;

// iterating over key-value pairs: for (std::map<std::string, int>::iterator it = myDict.begin(); it != myDict.end(); ++it) {

   // the thing pointed to by the iterator is an std::pair<const std::string, int>&
   const std::string& key = it->first;
   int& value = it->second;
   std::cout << "key = " << key << ", value = " << value << std::endl;

}</lang>

C#

<lang csharp>using System; using System.Collections.Generic;

namespace AssocArrays {

   class Program
   {
       static void Main(string[] args)
       {

           Dictionary<string,int> assocArray = new Dictionary<string,int>();

           assocArray["Hello"] = 1;
           assocArray.Add("World", 2);
           assocArray["!"] = 3;

           foreach (KeyValuePair<string, int> kvp in assocArray)
           {
               Console.WriteLine(kvp.Key + " : " + kvp.Value);
           }

           foreach (string key in assocArray.Keys)
           {
               Console.WriteLine(key);
           }

           foreach (int val in assocArray.Values)
           {
               Console.WriteLine(val.ToString());
           }
       }
   }

} </lang>

Chapel

<lang chapel>var A = [ "H2O" => "water", "NaCl" => "salt", "O2" => "oxygen" ];

for k in A.domain do

   writeln("have key: ", k);

for v in A do

   writeln("have value: ", v);

for (k,v) in zip(A.domain, A) do

   writeln("have element: ", k, " -> ", v);</lang>

Output:

have key: O2
have key: NaCl
have key: H2O
have value: oxygen
have value: salt
have value: water
have element: O2 -> oxygen
have element: NaCl -> salt
have element: H2O -> water

Clojure

<lang clojure> (doseq [[k v] {:a 1, :b 2, :c 3}]

 (println k "=" v))

(doseq [k (keys {:a 1, :b 2, :c 3})]

 (println k))

(doseq [v (vals {:a 1, :b 2, :c 3})]

 (println v))

</lang>

CoffeeScript

<lang coffeescript>hash =

 a: 'one'
 b: 'two'

for key, value of hash

 console.log key, value

for key of hash

 console.log key

</lang>

Common Lisp

Common Lisp has three common idioms for associating keys with values: association lists (alists), property lists (plists), and hash tables.

With association lists (alists)

The association list is a list of conses, each of whose car is a key and whose cdr is a value. The standard mapping and print functions can be used to print key/value pairs, keys, and values.

<lang lisp>;; iterate using dolist, destructure manually (dolist (pair alist)

 (destructuring-bind (key . value) pair
   (format t "~&Key: ~a, Value: ~a." key value)))

iterate and destructure with loop

(loop for (key . value) in alist

     do (format t "~&Key: ~a, Value: ~a." key value))</lang>

With property lists (plists)

Property lists are lists of alternating keys and values, where each value's key is the element of the list immediately following it. Printing could be done with standard mapping functions, but loop's destructuring makes things a bit easier.

<lang lisp>(loop for (key value) on plist :by 'cddr

     do (format t "~&Key: ~a, Value: ~a." key value))</lang>

With hash tables

Lisp also has built-in hash tables, and there are several ways to map over these. The first is maphash which takes a function of two arguments (the key and value) and the hash table.

<lang lisp>(maphash (lambda (key value)

          (format t "~&Key: ~a, Value: ~a." key value))
        hash-table)</lang>

The loop construct also supports extracting key/value pairs from hash tables.

<lang lisp>(loop for key being each hash-key of hash-table using (hash-value value)

     do (format t "~&Key: ~a, Value: ~a." key value))</lang>

There is also a macro with-hash-table-iterator which locally binds a name to produce associated keys and values of the hash table; while rarely used, it is the most powerful operation.

<lang lisp>(with-hash-table-iterator (next-entry hash-table)

 (loop
  (multiple-value-bind (nextp key value) (next-entry)
    (if (not nextp)
      (return)
      (format t "~&Key: ~a, Value: ~a." key value)))))</lang>

D

Works with: D version 2

<lang d>import std.stdio: writeln;

void main() {

   // the associative array
   auto aa = ["alice":2, "bob":97, "charlie":45];

   // how to iterate key/value pairs:
   foreach (key, value; aa)
       writeln("1) Got key ", key, " with value ", value);
   writeln();

   // how to iterate the keys:
   foreach (key, _; aa)
       writeln("2) Got key ", key);
   writeln();

   // how to iterate the values:
   foreach (value; aa)
       writeln("3) Got value ", value);
   writeln();

   // how to extract the values, lazy:
   foreach (value; aa.byValue())
       writeln("4) Got value ", value);
   writeln();

   // how to extract the keys, lazy:
   foreach (key; aa.byKey())
       writeln("5) Got key ", key);
   writeln();

   // how to extract all the keys:
   foreach (key; aa.keys)
       writeln("6) Got key ", key);
   writeln();

   // how to extract all the values:
   foreach (value; aa.values)
       writeln("7) Got value ", value);

}</lang>

Dao

<lang ruby> dict = { 'def' => 1, 'abc' => 2 }

for( keyvalue in dict ) io.writeln( keyvalue ); for( key in dict.keys(); value in dict.values() ) io.writeln( key, value ) dict.iterate { [key, value]

   io.writeln( key, value )

} </lang>

Delphi

<lang Delphi>program AssociativeArrayIteration;

{$APPTYPE CONSOLE}

uses SysUtils, Generics.Collections;

var

 i: Integer;
 s: string;
 lDictionary: TDictionary<string, Integer>;
 lPair: TPair<string, Integer>;

begin

 lDictionary := TDictionary<string, Integer>.Create;
 try
   lDictionary.Add('foo', 5);
   lDictionary.Add('bar', 10);
   lDictionary.Add('baz', 15);
   lDictionary.AddOrSetValue('foo', 6);

   for lPair in lDictionary do
     Writeln(Format('Pair: %s = %d', [lPair.Key, lPair.Value]));
   for s in lDictionary.Keys do
     Writeln('Key: ' + s);
   for i in lDictionary.Values do
     Writeln('Value: ', i);
 finally
   lDictionary.Free;
 end;

end.</lang>

E

In E, the basic iteration protocol and syntax work over key-value pairs. Therefore, any iteration over a map or other collection is always key-value, though the user may choose to ignore the keys or the values.

The for loop takes either one pattern, for the value, or two, for the key and value; for iterating over keys alone the value may be given an ignore-pattern (_).

<lang e>def map := [

 "a" => 1,
 "b" => 2,
 "c" => 3,

]

for key => value in map {

 println(`$key $value`)

}

for value in map { # ignore keys

 println(`. $value`)

}

for key => _ in map { # ignore values

 println(`$key .`)

}

for key in map.domain() { # iterate over the set whose values are the keys

 println(`$key .`)

}</lang>

Elena

<lang elena>#define system.

define system'collections.
define system'routines.
define extensions.

// --- Program ---

symbol program =

[

   // 1. Create
   #var aMap := Dictionary new.
   aMap@"key" := "foox".
   aMap@"key2":= "foo2".
   aMap@"key3":= "foo3".
   aMap@"key4":= "foo4".

   // Enumerate
   aMap run &each: aKeyValue
       [ console writeLine:(aKeyValue key):" : ":aKeyValue ].

].</lang>

Elixir

<lang elixir>defmodule RC do

 def test_iterate(dict_impl \\ Map) do
   d = dict_impl.new |> Dict.put(:foo,1) |> Dict.put(:bar,2)
   print_vals(d)
 end
 
 defp print_vals(d) do
   IO.inspect d
   Enum.each(d, fn {k,v} -> IO.puts "#{k}: #{v}" end)
   Enum.each(Dict.keys(d), fn key -> IO.inspect key end)
   Enum.each(Dict.values(d), fn value -> IO.inspect value end) 
 end

end

IO.puts "< iterate Map >" RC.test_iterate IO.puts "\n< iterate HashDict >" RC.test_iterate(HashDict)</lang>

Output:

< iterate Map >
%{bar: 2, foo: 1}
bar: 2
foo: 1
:bar
:foo
2
1

< iterate HashDict >
#HashDict<[foo: 1, bar: 2]>
foo: 1
bar: 2
:foo
:bar
1
2

Erlang

<lang erlang> -module(assoc). -compile([export_all]).

test_create() ->

   D = dict:new(),
   D1 = dict:store(foo,1,D),
   D2 = dict:store(bar,2,D1),
   print_vals(D2).

print_vals(D) ->

   lists:foreach(fun (K) ->
                         io:format("~p: ~b~n",[K,dict:fetch(K,D)])
                 end, dict:fetch_keys(D)).

</lang>

Output:

32> assoc:test_create().
bar: 2
foo: 1
ok

F#

Iterating over both. <lang fsharp> let myMap = [ ("Hello", 1); ("World", 2); ("!", 3) ]

for k, v in myMap do

 printfn "%s -> %d" k v

</lang>

Iterating over either keys or values only can be achieved through use of the _ wildcard token. <lang fsharp> // Only prints the keys. for k, _ in myMap do

   printfn "%s" k

// Only prints the values. for _, v in myMap do

   printfn "%d" v

</lang>

Factor

<lang factor>H{ { "hi" "there" } { "a" "b" } } [ ": " glue print ] assoc-each</lang> There's also assoc-map, assoc-find, assoc-filter and many more.

Fantom

Given a map, each iterates over pairs of values-keys. keys and vals retrieve a list of keys or values, respectively.

<lang fantom> class Main {

 public static Void main ()
 {
   Int:Str map := [1:"alpha", 2:"beta", 3:"gamma"]

   map.keys.each |Int key|
   {
     echo ("Key is: $key")
   }

   map.vals.each |Str value|
   {
     echo ("Value is: $value")
   }

   map.each |Str value, Int key|
   {
     echo ("Key $key maps to $value")
   }
 }

} </lang>

Forth

Library: Forth Foundation Library

<lang forth>include ffl/hct.fs include ffl/hci.fs

\ Create hashtable and iterator in dictionary 10 hct-create htable htable hci-create hiter

\ Insert entries 1 s" hello" htable hct-insert 2 s" world" htable hct-insert 3 s" !" htable hct-insert

iterate

 hiter hci-first
 BEGIN
 WHILE
   ." key = " hiter hci-key type ." , value = " . cr
   hiter hci-next
 REPEAT

iterate</lang>

<lang forth> \ Written in ANS-Forth; tested under VFX. \ Requires the novice package: http://www.forth.org/novice.html \ The following should already be done: \ include novice.4th \ include association.4th

\ I would define high-level languages as those that allow programs to be written without explicit iteration. Iteration is a major source of bugs. \ The example from the FFL library doesn't hide iteration, whereas this example from the novice-package does.

marker AssociationIteration.4th

\ ****** \ ****** The following defines a node in an association (each node is derived from ELEMENT). \ ******

element

   w field .inventor

constant language \ describes a programming language

init-language ( inventor name node -- node )

   init-element >r
   hstr r@ .inventor !
   r> ;

new-language ( inventor name -- node )

   language alloc
   init-language ;

show-language ( count node -- )

   >r
   1+                      \ -- count+1
   cr  r@ .key @ count colorless type  ." invented by: "  r@ .inventor @ count type
   rdrop ;

show-languages-forward ( handle -- )

   0                       \ -- handle count
   swap .root @  ['] show-language  walk> 
   cr ." count: " . 
   cr ;

show-languages-backward ( handle -- )

   0                       \ -- handle count
   swap .root @  ['] show-language  <walk
   cr ." count: " . 
   cr ;

kill-language-attachments ( node -- )

   dup .inventor @  dealloc
   kill-key ;

copy-language-attachments ( src dst -- )

   over .inventor @  hstr
   over .inventor !
   copy-key ;

\ ****** \ ****** The following defines the association itself (the handle). \ ******

association constant languages \ describes a set of programming languages

init-languages ( record -- record )

   >r
   ['] compare  ['] kill-language-attachments  ['] copy-language-attachments
   r> init-association ;

new-languages ( -- record )

   languages alloc
   init-languages ;

\ ****** \ ****** The following filters one association into another, including everything that matches a particular inventor. \ ******

<filter-inventor> { inventor handle new-handle node -- inventor handle new-handle }

   inventor count  node .inventor @ count  compare  A=B = if
       node handle dup-element  new-handle insert  then
   inventor handle new-handle ;

filter-inventor ( inventor handle -- new-handle )

   dup similar-association                             \ -- inventor handle new-handle 
   over .root @  ['] <filter-inventor>  walk>          \ -- inventor handle new-handle
   nip nip ;

\ ****** \ ****** The following is a demonstration with some sample data. \ ******

new-languages

   c" Moore, Chuck"                c" Forth     "      new-language  over insert
   c" Ichiah, Jean"                c" Ada       "      new-language  over insert
   c" Wirth, Niklaus"              c" Pascal    "      new-language  over insert
   c" Wirth, Niklaus"              c" Oberon    "      new-language  over insert
   c" McCarthy, John"              c" Lisp      "      new-language  over insert
   c" van Rossum, Guido"           c" Python    "      new-language  over insert
   c" Gosling, Jim"                c" Java      "      new-language  over insert
   c" Ierusalimschy, Roberto"      c" Lua       "      new-language  over insert
   c" Matsumoto, Yukihiro"         c" Ruby      "      new-language  over insert
   c" Pestov, Slava"               c" Factor    "      new-language  over insert
   c" Gosling, James"              c" Java      "      new-language  over insert
   c" Wirth, Niklaus"              c" Modula-2  "      new-language  over insert
   c" Ritchie, Dennis"             c" C         "      new-language  over insert
   c" Stroustrup, Bjarne"          c" C++       "      new-language  over insert

constant some-languages

cr .( everything in SOME-LANGUAGES ordered forward: )

some-languages show-languages-forward

cr .( everything in SOME-LANGUAGES ordered backward: )

some-languages show-languages-backward

cr .( everything in SOME-LANGUAGES invented by Wirth: )

c" Wirth, Niklaus" some-languages filter-inventor dup show-languages-forward kill-association

cr .( everything in SOME-LANGUAGES within 'F' and 'L': )

c" F" c" L" some-languages filter within dup show-languages-forward kill-association

cr .( everything in SOME-LANGUAGES not within 'F' and 'L': )

c" F" c" L" some-languages filter without dup show-languages-forward kill-association

some-languages kill-association </lang>

Output:

everything in SOME-LANGUAGES ordered forward: 
Ada       invented by: Ichiah, Jean
C         invented by: Ritchie, Dennis
C++       invented by: Stroustrup, Bjarne
Factor    invented by: Pestov, Slava
Forth     invented by: Moore, Chuck
Java      invented by: Gosling, James
Lisp      invented by: McCarthy, John
Lua       invented by: Ierusalimschy, Roberto
Modula-2  invented by: Wirth, Niklaus
Oberon    invented by: Wirth, Niklaus
Pascal    invented by: Wirth, Niklaus
Python    invented by: van Rossum, Guido
Ruby      invented by: Matsumoto, Yukihiro
count: 13 

everything in SOME-LANGUAGES ordered backward: 
Ruby      invented by: Matsumoto, Yukihiro
Python    invented by: van Rossum, Guido
Pascal    invented by: Wirth, Niklaus
Oberon    invented by: Wirth, Niklaus
Modula-2  invented by: Wirth, Niklaus
Lua       invented by: Ierusalimschy, Roberto
Lisp      invented by: McCarthy, John
Java      invented by: Gosling, James
Forth     invented by: Moore, Chuck
Factor    invented by: Pestov, Slava
C++       invented by: Stroustrup, Bjarne
C         invented by: Ritchie, Dennis
Ada       invented by: Ichiah, Jean
count: 13 

everything in SOME-LANGUAGES invented by Wirth: 
Modula-2  invented by: Wirth, Niklaus
Oberon    invented by: Wirth, Niklaus
Pascal    invented by: Wirth, Niklaus
count: 3 

everything in SOME-LANGUAGES within 'F' and 'L': 
Factor    invented by: Pestov, Slava
Forth     invented by: Moore, Chuck
Java      invented by: Gosling, James
count: 3 

everything in SOME-LANGUAGES not within 'F' and 'L': 
Ada       invented by: Ichiah, Jean
C         invented by: Ritchie, Dennis
C++       invented by: Stroustrup, Bjarne
Lisp      invented by: McCarthy, John
Lua       invented by: Ierusalimschy, Roberto
Modula-2  invented by: Wirth, Niklaus
Oberon    invented by: Wirth, Niklaus
Pascal    invented by: Wirth, Niklaus
Python    invented by: van Rossum, Guido
Ruby      invented by: Matsumoto, Yukihiro
count: 10

Go

<lang go>myMap := map[string]int { "hello": 13, "world": 31, "!" : 71 }

// iterating over key-value pairs: for key, value := range myMap {

   fmt.Printf("key = %s, value = %d\n", key, value)

}

// iterating over keys: for key := range myMap {

   fmt.Printf("key = %s\n", key)

}

// iterating over values: for _, value := range myMap {

   fmt.Printf("value = %d\n", value)

}</lang>

Groovy

Solution: <lang groovy>def map = [lastName: "Anderson", firstName: "Thomas", nickname: "Neo", age: 24, address: "everywhere"]

println "Entries:" map.each { println it }

println() println "Keys:" map.keySet().each { println it }

println() println "Values:" map.values().each { println it }</lang>

Output:

Entries:
lastName=Anderson
firstName=Thomas
nickname=Neo
age=24
address=everywhere

Keys:
lastName
firstName
nickname
age
address

Values:
Anderson
Thomas
Neo
24
everywhere

Harbour

<lang visualfoxpro>LOCAL arr := { 6 => 16, "eight" => 8, "eleven" => 11 } LOCAL x

FOR EACH x IN arr

  // key, value
  ? x:__enumKey(), x
  // or key only
  ? x:__enumKey()
  // or value only
  ? x

NEXT</lang>

Haskell

with Data.Map: <lang haskell>import qualified Data.Map as M

myMap = M.fromList [("hello", 13), ("world", 31), ("!", 71)]

main = do -- pairs

         print $ M.toList myMap
         -- keys
         print $ M.keys myMap
         -- values
         print $ M.elems myMap</lang>

Icon and Unicon

<lang icon>procedure main()

   t := table()
   every t[a := !"ABCDE"] := map(a)

   every pair := !sort(t) do
       write("\t",pair[1]," -> ",pair[2])

   writes("Keys:")
   every writes(" ",key(t))
   write()

   writes("Values:")
   every writes(" ",!t)
   write()

end</lang>

Output:

->aai
        A -> a
        B -> b
        C -> c
        D -> d
        E -> e
Keys: C E B D A
Values: c e b d a

J

Note that all J operations either iterate over the items of an array or can be made to do so. So to iterate over some sequence you need to refer to that sequence.

Using the J example from Creating an Associative Array...

Keys <lang J>nl__example 0</lang>

Values <lang J>get__example each nl__example 0</lang>

Both keys and values <lang J>(,&< get__example) each nl__example 0</lang>

Note that this last is not likely to be useful in any practical context outside of learning the language.

Java

<lang java>Map<String, Integer> myDict = new HashMap<String, Integer>(); myDict.put("hello", 1); myDict.put("world", 2); myDict.put("!", 3);

// iterating over key-value pairs: for (Map.Entry<String, Integer> e : myDict.entrySet()) {

   String key = e.getKey();
   Integer value = e.getValue();
   System.out.println("key = " + key + ", value = " + value);

}

// iterating over keys: for (String key : myDict.keySet()) {

   System.out.println("key = " + key);

}

// iterating over values: for (Integer value : myDict.values()) {

   System.out.println("value = " + value);

}</lang>

Java 8 version

<lang java>Map<String, Integer> myDict = new HashMap<>(); myDict.put("hello", 1); myDict.put("world", 2); myDict.put("!", 3);

// iterating over key-value pairs: myDict.forEach((k, v) -> {

   System.out.printf("key = %s, value = %s%n", k, v);

});

// iterating over keys: myDict.keySet().forEach(k -> System.out.printf("key = %s%n", k));

// iterating over values: myDict.values().forEach(v -> System.out.printf("value = %s%n", v));</lang>

key = !, value = 3
key = world, value = 2
key = hello, value = 1
key = !
key = world
key = hello
value = 3
value = 2
value = 1

JavaScript

JavaScript does not have associative arrays until ECMAScript 6 brings Maps. In versions up to ES5.1, you may add properties to an empty object to achieve the same effect. <lang javascript>var myhash = {}; //a new, empty object myhash["hello"] = 3; myhash.world = 6; //obj.name is equivalent to obj["name"] for certain values of name myhash["!"] = 9;

//iterate using for..in loop for (var key in myhash) {

 //ensure key is in object and not in prototype
 if (myhash.hasOwnProperty(key)) {
   console.log("Key is: " + key + '. Value is: ' + myhash[key]);
 }

}

//iterate using ES5.1 Object.keys() and Array.prototype.Map() var keys = Object.keys(); //get Array of object keys (doesn't get prototype keys) keys.map(function (key) {

 console.log("Key is: " + key + '. Value is: ' + myhash[key]);

});</lang>

Jq

In jq, there are several ways to iterate over compound structures:

- functionally, e.g. using map on an array
- by enumeration, i.e. by generating a stream
- by performing a reduction

For the sake of brevity, therefore, in the following we will only illustrate the enumerative approach.

With respect to associative arrays (i.e. JSON objects), the fundamental functions are:

- keys -- for producing an array of the keys (sorted) 
- .[]  -- for producing a stream of the values

In jq > 1.4, keys_unsorted, for producing an array of the keys (in the order of creation), is also available. <lang jq>def mydict: {"hello":13, "world": 31, "!": 71};

Iterating over the keys

mydict | keys[]

"!"
"hello"
"world"

Iterating over the values:

mydict[]

13
31
71

Generating a stream of {"key": key, "value": value} objects:

mydict | to_entries[]

{"key":"hello","value":13}
{"key":"world","value":31}
{"key":"!","value":71}

Generating a stream of [key,value] arrays:

mydict | . as $o | keys[] | [., $o[.]]

["!",71]
["hello",13]
["world",31]

Generating a stream of [key,value] arrays, without sorting (jq > 1.4 required)

mydict | . as $o | keys_unsorted[] | [., $o[.]]

["hello",13]
["world",31]
["!",71]

</lang>

Julia

Translation of: Python

<lang julia>mydict = [ "hello"=>13, "world"=>31, "!"=>71 ]

applying a function to key-value pairs:

map(println, mydict);

iterating over key-value pairs:

for (key,value) in mydict

 println("key = $key, value = $value")

end

iterating over keys:

for key in keys(mydict)

 println("key = $key")

end

iterating over values:

for value in values(mydict)

 println("value = $value")

end</lang>

Output:

key = !, value = 71
key = hello, value = 13
key = world, value = 31
key = !
key = hello
key = world
value = 71
value = 13
value = 31

K

Creating a dictionary. <lang K> d: .((`"hello";1); (`"world";2);(`"!";3))</lang>

The keys are available via "!". <lang K> !d `hello `world `"!"

  $!d  / convert keys (symbols) as strings

("hello"

"world"
,"!")</lang>

Print the key value pairs. <lang K> `0:{,/$x,": ",d[x]}'!d hello: 1 world: 2 !: 3</lang>

The values are available via "[]". <lang K> d[] 1 2 3

 {x+1}'d[]

2 3 4</lang>

Lang5

<lang lang5>: first 0 extract nip ; : second 1 extract nip ; : nip swap drop ;

say(*) dup first " => " 2 compress "" join . second . ;

[['foo 5] ['bar 10] ['baz 20]] 'say apply drop</lang>

Lasso

<lang Lasso> //iterate over associative array //Lasso maps local('aMap' = map('weight' = 112, 'height' = 45, 'name' = 'jason')) ' Map output: \n ' #aMap->forEachPair => {^ //display pair, then show accessing key and value individually #1+'\n ' #1->first+': '+#1->second+'\n ' ^} //display keys and values separately '\n' ' Map Keys: '+#aMap->keys->join(',')+'\n' ' Map values: '+#aMap->values->join(',')+'\n'

//display using forEach '\n' ' Use ForEach to iterate Map keys: \n' #aMap->keys->forEach => {^ #1+'\n' ^} '\n' ' Use ForEach to iterate Map values: \n' #aMap->values->forEach => {^ #1+'\n' ^} //the {^ ^} indicates that output should be printed (AutoCollect) , // if output is not desired, just { } is used </lang>

LFE

Keys and Values

<lang lisp> (let ((data '(#(key1 "foo") #(key2 "bar")))

     (hash (: dict from_list data)))
 (: dict fold 
   (lambda (key val accum) 
     (: io format '"~s: ~s~n" (list key val)))
   0
   hash))

</lang>

Just Keys

<lang lisp> (let ((data '(#(key1 "foo") #(key2 "bar")))

     (hash (: dict from_list data)))
 (: lists map 
   (lambda (key) 
     (: io format '"~s~n" (list key))) 
   (: dict fetch_keys hash)))

</lang>

Liberty BASIC

Needs the sublist library from http://basic.wikispaces.com/SubList+Library since LB does not have built-in associative arrays. <lang lb> data "red", "255 50 50", "green", "50 255 50", "blue", "50 50 255" data "my fave", "220 120 120", "black", "0 0 0"

myAssocList$ =""

for i =1 to 5

   read k$
   read dat$
   call sl.Set myAssocList$, k$, dat$

next i

keys$ = "" ' List to hold the keys in myList$. keys = 0

keys = sl.Keys( myAssocList$, keys$) print " Number of key-data pairs ="; keys

For i = 1 To keys

   keyName$ = sl.Get$( keys$, Str$( i))
   Print "  Key "; i; ":", keyName$, "Data: ", sl.Get$( myAssocList$, keyName$)

Next i

end </lang>

 Number of key-data pairs =5
 Key 1:      red           Data:         255 50 50
 Key 2:      green         Data:         50 255 50
 Key 3:      blue          Data:         50 50 255
 Key 4:      my fave       Data:         220 120 120
 Key 5:      black         Data:         0 0 0

Lua

<lang lua>local t = {

   ["foo"] = "bar",
   ["baz"] = 6,
   fortytwo = 7

}

for key,val in pairs(t) do

   print(string.format("%s: %s", key, val))

end</lang>

Output:

    fortytwo: 7
    foo: bar
    baz: 6

Note: the order in which pairs iterates over non-integer keys is not defined, so the order of lines in the output of the above code may differ from one run to another.

M4

<lang M4>divert(-1) define(`for',

  `ifelse($#,0,``$0,
  `ifelse(eval($2<=$3),1,
  `pushdef(`$1',$2)$4`'popdef(`$1')$0(`$1',incr($2),$3,`$4')')')')

define(`new',`define(`$1[size]key',0)') define(`asize',`defn(`$1[size]key')') define(`aget',`defn(`$1[$2]')') define(`akget',`defn(`$1[$2]key')') define(`avget',`aget($1,akget($1,$2))') define(`aset',

  `ifdef($1[$2],
     `',
     `define(`$1[size]key',incr(asize(`$1')))`'define($1[asize(`$1')]key,$2)')`'define($1[$2],$3)')

define(`dquote', ``$@) define(`akeyvalue',`dquote(akget($1,$2),aget($1,akget($1,$2)))') define(`akey',`dquote(akget($1,$2))') define(`avalue',`dquote(aget($1,akget($1,$2)))') divert new(`a') aset(`a',`wow',5) aset(`a',`wow',flame) aset(`a',`bow',7) key-value pairs for(`x',1,asize(`a'),

  `akeyvalue(`a',x)

') keys for(`x',1,asize(`a'),

  `akey(`a',x)

') values for(`x',1,asize(`a'),

  `avalue(`a',x)

')</lang>

Output:

key-value pairs
`wow',`flame'
`bow',`7'

keys
`wow'
`bow'

values
`flame'
`7'

Maple

Iterate through indices when indices are all simple expressions: <lang Maple> > T := table( [ "A" = 1, "B" = 2, "C" = 3, "D" = 4 ] ); > for i in indices( T, nolist ) do print(i ) end:

"A"

"B"

"C"

"D"

</lang>

Iterate through indices when indices may be expression sequences: <lang Maple> > T := table( [ "a" = 1, "b" = 2, ("c","d") = 3 ] ): > for i in indices( T ) do print( i, T[ op( i ) ] ) end:

                               ["a"], 1

                               ["b"], 2

                            ["c", "d"], 3

</lang>

Return all index / entry pairs as equations: <lang Maple> > for i in indices( T, pairs ) do print( i) end:

                               "a" = 1

                               "b" = 2

                            ("c", "d") = 3

</lang>

<lang Maple> > for i in entries( T ) do print( i) end:

[1]

[3]

[2]

</lang>

Mathematica

<lang Mathematica>keys=DownValues[#,Sort->False]All,1,1,1&; hashes=#/@keys[#]&;

a[2]="string";a["sometext"]=23; keys[a] ->{2,sometext} hashes[a] ->{string,23}</lang>

MATLAB / Octave

Associative arrays can be defined as structs in Matlab and Octave.

<lang Matlab> keys = fieldnames(hash);

  for k=1:length(keys), 
       key = keys{k};

value = getfield(hash,key); % get value of key hash = setfield(hash,key,-value); % set value of key

  end; </lang>

or

<lang Matlab> keys = fieldnames(hash);

  for k=1:length(keys), 
       key = keys{k};
       value = hash.(key);     % get value of key
       hash.(key) = -value;    % set value of key
  end; </lang>

Maxima

<lang Maxima>h[1]: 6$ h[9]: 2$

/* iterate over values */ for val in listarray(h) do (

 print(val))$

/* iterate over the keys */ for key in rest(arrayinfo(h), 2) do (

 val: arrayapply(h, key),
 print(key, val))$</lang>

NetRexx

<lang NetRexx>/* NetRexx */ options replace format comments java crossref symbols

surname = 'Unknown' -- default value surname['Fred'] = 'Bloggs' surname['Davy'] = 'Jones'

try = 'Fred' say surname[try] surname['Bert']

-- extract the keys loop fn over surname

 say fn.right(10) ':' surname[fn]
 end fn</lang>

NewLISP

<lang NewLISP>;; using an association list: (setq alist '(("A" "a") ("B" "b") ("C" "c")))

list keys

(map first alist)

list values

(map last alist)

loop over the assocation list

(dolist (elem alist)

 (println (format "%s -> %s" (first elem) (last elem))))</lang>

Nim

<lang nim> import tables

var t: TTable[int,string] = initTable[int,string]()

t[1] = "one" t[2] = "two" t[3] = "three" t.add(4,"four")

echo "t has " & $t.len & " elements"

echo "has t key 4? " & $t.hasKey(4) echo "has t key 5? " & $t.hasKey(5)

iterate keys

echo "key iteration:" for k in t.keys:

 echo "at[" & $k & "]=" & t[k]

itetate pairs

echo "pair iteration:" for k,v in t.pairs:

 echo "at[" & $k & "]=" & v

</lang>

Output:

t has 4 elements
has t key 4? true
has t key 5? false
key iteration:
at[1]=one
at[2]=two
at[3]=three
at[4]=four
pair iteration:
at[1]=one
at[2]=two
at[3]=three
at[4]=four

Oberon-2

Works with: oo2c Version 2

<lang oberon2> MODULE AssociativeArray; IMPORT

 ADT:Dictionary,
 Object:Boxed,
 Out;

TYPE

 Key = STRING;
 Value = Boxed.LongInt;

VAR

 assocArray: Dictionary.Dictionary(Key,Value);
 iterK: Dictionary.IterKeys(Key,Value);
 iterV: Dictionary.IterValues(Key,Value);
 aux: Value;
 k: Key;

BEGIN

 assocArray := NEW(Dictionary.Dictionary(Key,Value));
 assocArray.Set("ten",NEW(Value,10));
 assocArray.Set("eleven",NEW(Value,11));
 
 aux := assocArray.Get("ten");
 Out.LongInt(aux.value,0);Out.Ln;
 aux := assocArray.Get("eleven");
 Out.LongInt(aux.value,0);Out.Ln;Out.Ln;
 
 (* Iterate keys *)
 iterK := assocArray.IterKeys();
 WHILE (iterK.Next(k)) DO
   Out.Object(k);Out.Ln
 END;
 
 Out.Ln;
 
 (* Iterate values *)
 iterV := assocArray.IterValues();
 WHILE (iterV.Next(aux)) DO
   Out.LongInt(aux.value,0);Out.Ln
 END

END AssociativeArray. </lang>

Objeck

<lang objeck> class Iteration {

 function : Main(args : String[]) ~ Nil {
   assoc_array := Collection.StringMap->New();
   assoc_array->Insert("Hello", IntHolder->New(1));
   assoc_array->Insert("World", IntHolder->New(2));
   assoc_array->Insert("!", IntHolder->New(3));

   keys := assoc_array->GetKeys();
   values := assoc_array->GetValues();

   each(i : keys) {
     key := keys->Get(i)->As(String);
     value := assoc_array->Find(key)->As(IntHolder)->Get();
     "key={$key}, value={$value}"->PrintLine();
   };

   "-------------"->PrintLine();

   each(i : keys) {
     key := keys->Get(i)->As(String);
     value := values->Get(i)->As(IntHolder)->Get();
     "key={$key}, value={$value}"->PrintLine();
   };
 }

} </lang>

Objective-C

Works with: Objective-C version 2.0+

<lang objc>NSDictionary *myDict = [NSDictionary dictionaryWithObjectsAndKeys:

                       [NSNumber numberWithInt:13], @"hello",
                       [NSNumber numberWithInt:31], @"world",
                       [NSNumber numberWithInt:71], @"!", nil];

// iterating over keys: for (id key in myDict) {

   NSLog(@"key = %@", key);

}

// iterating over values: for (id value in [myDict objectEnumerator]) {

   NSLog(@"value = %@", value);

}</lang>

Works with: Objective-C version <2.0

<lang objc>NSDictionary *myDict = [NSDictionary dictionaryWithObjectsAndKeys:

                       [NSNumber numberWithInt:13], @"hello",
                       [NSNumber numberWithInt:31], @"world",
                       [NSNumber numberWithInt:71], @"!", nil];

// iterating over keys: NSEnumerator *enm = [myDict keyEnumerator]; id key; while ((key = [enm nextObject])) {

   NSLog(@"key = %@", key);

}

// iterating over values: enm = [myDict objectEnumerator]; id value; while ((value = [enm nextObject])) {

   NSLog(@"value = %@", value);

}</lang>

Works with: Cocoa version Mac OS X 10.6+

<lang objc>NSDictionary *myDict = [NSDictionary dictionaryWithObjectsAndKeys:

                       [NSNumber numberWithInt:13], @"hello",
                       [NSNumber numberWithInt:31], @"world",
                       [NSNumber numberWithInt:71], @"!", nil];

// iterating over keys and values: [myDict enumerateKeysAndObjectsUsingBlock: ^(id key, id value, BOOL *stop) {

   NSLog(@"key = %@, value = %@", key, value);

}];</lang>

OCaml

Association array: <lang ocaml>#!/usr/bin/env ocaml

let map = [| ('A', 1); ('B', 2); ('C', 3) |] ;;

(* iterate over pairs *) Array.iter (fun (k,v) -> Printf.printf "key: %c - value: %d\n" k v) map ;;

(* iterate over keys *) Array.iter (fun (k,_) -> Printf.printf "key: %c\n" k) map ;;

(* iterate over values *) Array.iter (fun (_,v) -> Printf.printf "value: %d\n" v) map ;;

(* in functional programming it is often more useful to fold over the elements *) Array.fold_left (fun acc (k,v) -> acc ^ Printf.sprintf "key: %c - value: %d\n" k v) "Elements:\n" map ;;</lang>

Hash table: <lang ocaml>let map = Hashtbl.create 42;; Hashtbl.add map 'A' 1;; Hashtbl.add map 'B' 2;; Hashtbl.add map 'C' 3;;

(* iterate over pairs *) Hashtbl.iter (fun k v -> Printf.printf "key: %c - value: %d\n" k v) map ;;

(* in functional programming it is often more useful to fold over the elements *) Hashtbl.fold (fun k v acc -> acc ^ Printf.sprintf "key: %c - value: %d\n" k v) map "Elements:\n" ;;</lang>

Functional binary search tree: <lang ocaml>module CharMap = Map.Make (Char);; let map = CharMap.empty;; let map = CharMap.add 'A' 1 map;; let map = CharMap.add 'B' 2 map;; let map = CharMap.add 'C' 3 map;;

(* iterate over pairs *) CharMap.iter (fun k v -> Printf.printf "key: %c - value: %d\n" k v) map ;;

(* in functional programming it is often more useful to fold over the elements *) CharMap.fold (fun k v acc -> acc ^ Printf.sprintf "key: %c - value: %d\n" k v) map "Elements:\n" ;;</lang>

ooRexx

<lang oorexx> d = .directory~new d["hello"] = 1 d["world"] = 2 d["!"] = 3

-- iterating over keys: loop key over d

   say "key =" key

end

-- iterating over values: loop value over d~allitems

   say "value =" value

end

-- iterating over key-value pairs: s = d~supplier loop while s~available

   say "key =" s~index", value =" s~item
   s~next

end </lang>

Oz

<lang oz>declare

 MyMap = unit('hello':13 'world':31 '!':71)

in

 {ForAll {Record.toListInd MyMap} Show}  %% pairs
 {ForAll {Record.arity     MyMap} Show}  %% keys
 {ForAll {Record.toList    MyMap} Show}  %% values</lang>

PARI/GP

Works with: PARI/GP version 2.8.1+

The keys can be retried from a map with Vec: <lang parigp>keys = Vec(M);</lang> You can iterate over the values as usual: <lang parigp>for(i=1,#keys,

 print(keys[i]," ",mapget(M,keys[i]))

)</lang>

Perl

<lang perl>#! /usr/bin/perl use strict;

my %pairs = ( "hello" => 13, "world" => 31, "!" => 71 );

iterate over pairs

Be careful when using each(), however, because it uses a global iterator
associated with the hash. If you call keys() or values() on the hash in the
middle of the loop, the each() iterator will be reset to the beginning. If
you call each() on the hash somewhere in the middle of the loop, it will
skip over elements for the "outer" each(). Only use each() if you are sure
that the code inside the loop will not call keys(), values(), or each().

while ( my ($k, $v) = each %pairs) {

   print "(k,v) = ($k, $v)\n";

}

iterate over keys

foreach my $key ( keys %pairs ) {

   print "key = $key, value = $pairs{$key}\n";

}

or (see note about each() above)

while ( my $key = each %pairs) {

   print "key = $key, value = $pairs{$key}\n";

}

iterate over values

foreach my $val ( values %pairs ) {

   print "value = $val\n";

}</lang>

Perl 6

Works with: Rakudo version #21 "Seattle"

<lang perl6>my %pairs = hello => 13, world => 31, '!' => 71;

for %pairs.kv -> $k, $v {

   say "(k,v) = ($k, $v)";

}

{ say "$^a => $^b" } for %pairs.kv;

say "key = $_" for %pairs.keys;

say "value = $_" for %pairs.values;</lang>

PHP

<lang php><?php $pairs = array( "hello" => 1, "world" => 2, "!" => 3 );

// iterate over key-value pairs foreach($pairs as $k => $v) {

 echo "(k,v) = ($k, $v)\n";

}

// iterate over keys foreach(array_keys($pairs) as $key) {

 echo "key = $key, value = $pairs[$key]\n";

}

// iterate over values foreach($pairs as $value) {

 echo "values = $value\n";

} ?></lang>

PicoLisp

Using properties

<lang PicoLisp>(put 'A 'foo 5) (put 'A 'bar 10) (put 'A 'baz 15)

(getl 'A) # Get the whole property list

-> ((15 . baz) (10 . bar) (5 . foo))

(mapcar cdr (getl 'A)) # Get all keys

-> (baz bar foo)

(mapcar car (getl 'A)) # Get all values

-> (15 10 5)</lang>

Using an index tree

<lang PicoLisp>(idx 'A (def "foo" 5) T) (idx 'A (def "bar" 10) T) (idx 'A (def "baz" 15) T)

A # Get the whole tree

-> ("foo" ("bar" NIL "baz"))

(idx 'A) # Get all keys

-> ("bar" "baz" "foo")

(mapcar val (idx 'A)) # Get all values

-> (10 15 5)</lang>

Pike

note that the order is not alphabetic but depends on the hash value of the keys. the order is deterministic however.

<lang Pike> mapping(string:string) m = ([ "A":"a", "B":"b", "C":"c" ]); foreach(m; string key; string value) {

   write(key+value);

} Result: BbAaCc

// only keys foreach(m; string key;) {

   write(key);

} Result: BAC

// only values foreach(m;; string value) {

   write(value);

} Result: bac

</lang>

PostScript

<lang postscript> % over keys and values <</a 1 /b 2 /c 3>> {= =} forall % just keys <</a 1 /b 2 /c 3>> {= } forall % just values <</a 1 /b 2 /c 3>> {pop =} forall </lang>

PowerShell

Using the following hash table: <lang powershell>$h = @{ 'a' = 1; 'b' = 2; 'c' = 3 }</lang> Iterating over the key/value pairs is slightly cumbersome as it requires an explicit call to GetEnumerator: <lang powershell>$h.GetEnumerator() | ForEach-Object { Write-Host Key: $_.Name, Value: $_.Value }</lang> A foreach statement can also be used: <lang powershell>foreach ($e in $h.GetEnumerator()) {

   Write-Host Key: $e.Name, Value: $e.Value

}</lang> Iterating over the keys: <lang powershell>$h.Keys | ForEach-Object { Write-Host Key: $_ }

foreach ($k in $h.Keys) {

   Write-Host Key: $k

}</lang> Iterating over the values: <lang powershell>$h.Values | ForEach-Object { Write-Host Value: $_ }

foreach ($v in $h.Values) {

   Write-Host Value: $v

}</lang>

Prolog

Following the example at Associative Array Creation (with the understanding that using a predicate to store a hash does not prevent a "key" from having more than one value):

<lang prolog> assert( mymap(key1,value1) ). assert( mymap(key2,value1) ). </lang>

To perform the specific task at hand: <lang prolog> ?- forall( mymap(Key,Value), writeln( [Key,Value]) ).

[key1,value1] [key2,value1] </lang>

In Prolog, however, iteration is "built-in". For example: <lang prolog> ?- mymap(key1, Y). Y = value1.

?- mymap(X, value1). X = key1 ; X = key2. </lang>

To construct the list of keys: <lang prolog> ?- findall( X, mymap(X,value1), Xs). Xs = [key1, key2]. </lang>

To construct the list of distinct values: <lang prolog> ?- findall( Y, mymap(key1,Y), Ys). Ys = [value1]. </lang>

PureBasic

Hashes are a built-in type called Map in Purebasic.

<lang purebasic>NewMap dict.s() dict("de") = "German" dict("en") = "English" dict("fr") = "French"

ForEach dict()

 Debug MapKey(dict()) + ":" + dict()

Next</lang>

Python

<lang python>myDict = { "hello": 13, "world": 31, "!" : 71 }

iterating over key-value pairs:

for key, value in myDict.items():

   print ("key = %s, value = %s" % (key, value))

iterating over keys:

for key in myDict:

   print ("key = %s" % key)

(is a shortcut for:)

for key in myDict.keys():

   print ("key = %s" % key)

iterating over values:

for value in myDict.values():

   print ("value = %s" % value)</lang>

R

R lacks a native representation of key-value pairs, but different structures allow named elements, which provide similar functionality.

environment example

[1] 123

<lang r>> index <- "1" > envindex <- "rainfed hay" > for (name in ls(env)) { + cat(sprintf('index=%s, value=%s\n', name, envname)) + }</lang>

index=1, value=rainfed hay
index=x, value=123

vector example

<lang r>> x <- c(hello=1, world=2, "!"=3) > print(x["!"])</lang>

! 
3

<lang r>> print(unname(x["!"]))</lang>

[1] 3

list example

<lang R>> a <- list(a=1, b=2, c=3.14, d="xyz") > print(a$a)</lang>

[1] 1

<lang R>> print(a$d)</lang>

[1] "xyz"

Racket

Using the dictionary interface, different data structures can be treated as an associative array in Racket.

lang racket

(define dict1 #hash((apple . 5) (orange . 10))) ; hash table (define dict2 '((apple . 5) (orange . 10))) ; a-list (define dict3 (vector "a" "b" "c")) ; vector (integer keys)

(dict-keys dict1) ; => '(orange apple) (dict-values dict2) ; => '(5 10) (for/list ([(k v) (in-dict dict3)]) ; => '("0 -> a" "1 -> b" "2 -> c")

 (format "~a -> ~a" k v))

</lang>

REXX

<lang rexx>/*REXX program shows how to set/display values for an associative array.*/ /*┌────────────────────────────────────────────────────────────────────┐

 │ The (below) two REXX statements aren't really necessary,  but it   │
 │ shows how to define any and all entries in a associative array so  │
 │ that if a "key" is used that isn't defined, it can be displayed to │
 │ indicate such,  or its value can be checked to determine if a      │
 │ particular associative array element has been set (defined).       │
 └────────────────────────────────────────────────────────────────────┘*/

stateF.=' [not defined yet] ' /*sets any/all state former caps.*/ stateN.=' [not defined yet] ' /*sets any/all state names. */ /*┌────────────────────────────────────────────────────────────────────┐

 │ In REXX, when a "key" is used, it's normally stored (internally)   │
 │ as uppercase characters (as in the examples below).  Actually, any │
 │ characters can be used,  including blank(s) and non-displayable    │
 │ characters  (including '00'x, 'ff'x, commas, periods, quotes, ···).│
 └────────────────────────────────────────────────────────────────────┘*/

stateL= /*list of states (empty now). It's nice to be in alpha-*/

               /*betic order; they'll be listed in this order.  With a */
               /*little more code, they could be sorted quite easily.  */

call setSC 'al', "Alabama" ,'Tuscaloosa' call setSC 'ca', "California" ,'Benicia' call setSC 'co', "Colorado" ,'Denver City' call setSC 'ct', "Connecticut" ,'Hartford and New Haven (joint)' call setSC 'de', "Delaware" ,'New-Castle' call setSC 'ga', "Georgia" ,'Milledgeville' call setSC 'il', "Illinois" ,'Vandalia' call setSC 'in', "Indiana" ,'Corydon' call setSC 'ia', "Iowa" ,'Iowa City' call setSC 'la', "Louisiana" ,'New Orleans' call setSC 'me', "Maine" ,'Portland' call setSC 'mi', "Michigan" ,'Detroit' call setSC 'ms', "Mississippi" ,'Natchez' call setSC 'mo', "Missoura" ,'Saint Charles' call setSC 'mt', "Montana" ,'Virginia City' call setSC 'ne', "Nebraska" ,'Lancaster' call setSC 'nh', "New Hampshire" ,'Exeter' call setSC 'ny', "New York" ,'New York' call setSC 'nc', "North Carolina" ,'Fayetteville' call setSC 'oh', "Ohio" ,'Chillicothe' call setSC 'ok', "Oklahoma" ,'Guthrie' call setSC 'pa', "Pennsylvania" ,'Lancaster' call setSC 'sc', "South Carolina" ,'Charlestown' call setSC 'tn', "Tennessee" ,'Murfreesboro' call setSC 'vt', "Vermont" ,'Windsor'

     do j=1  for words(stateL)        /*show all capitals that were set*/
     q=word(stateL,j)                 /*get the next state in the list.*/
     say 'the former capital of  ('q") "    stateN.q   " was "   stateC.q
     end    /*j*/                     /* [↑]  display states defined.  */

exit /*stick a fork in it, we're done.*/ /*─────────────────────────────────────setSC subroutine─────────────────*/ setSC: arg code; parse arg ,name,cap /*get upper code, get name & cap.*/ stateL=stateL code /*keep a list of all state codes.*/ stateN.code=name /*set the state's name. */ stateC.code=cap /*set the state's capital. */ return /*return to invoker, SET is done.*/</lang>

Output:

the former capital of  (AL)  Alabama  was  Tuscaloosa
the former capital of  (CA)  California  was  Benicia
the former capital of  (CO)  Colorado  was  Denver City
the former capital of  (CT)  Connecticut  was  Hartford and New Haven (joint)
the former capital of  (DE)  Delaware  was  New-Castle
the former capital of  (GA)  Georgia  was  Milledgeville
the former capital of  (IL)  Illinois  was  Vandalia
the former capital of  (IN)  Indiana  was  Corydon
the former capital of  (IA)  Iowa  was  Iowa City
the former capital of  (LA)  Louisiana  was  New Orleans
the former capital of  (ME)  Maine  was  Portland
the former capital of  (MI)  Michigan  was  Detroit
the former capital of  (MS)  Mississippi  was  Natchez
the former capital of  (MO)  Missoura  was  Saint Charles
the former capital of  (MT)  Montana  was  Virginia City
the former capital of  (NE)  Nebraska  was  Lancaster
the former capital of  (NH)  New Hampshire  was  Exeter
the former capital of  (NY)  New York  was  New York
the former capital of  (NC)  North Carolina  was  Fayetteville
the former capital of  (OH)  Ohio  was  Chillicothe
the former capital of  (OK)  Oklahoma  was  Guthrie
the former capital of  (PA)  Pennsylvania  was  Lancaster
the former capital of  (SC)  South Carolina  was  Charlestown
the former capital of  (TN)  Tennessee  was  Murfreesboro
the former capital of  (VT)  Vermont  was  Windsor

When this example was started, the intention was to list the former capitals by key. Unfortunately, there's a duplicate (Lancaster).

RLaB

Associative arrays are called lists in RLaB.

<lang RLaB> x = <<>>; // create an empty list x.hello = 1; x.world = 2; x.["!"] = 3;

// to iterate over identifiers of a list one needs to use the function members // the identifiers are returned as a lexicographically ordered string row-vector // here ["!", "hello", "world"] for(i in members(x)) { printf("%s %g\n", i, x.[i]); }

// occasionally one needs to check if there exists member of a list y = members(x); // y contains ["!", "hello", "world"] clear(x.["!"]); // remove member with identifier "!" from the list "x" for(i in y) { printf("%s %g\n", i, x.[i]); } // this produces error because x.["!"] does not exist

for(i in y) {

 if (exist(x.[i]))
 { printf("%s %g\n", i,  x.[i]); }  // we print a member of the list "x" only if it exists

}

</lang>

Ruby

<lang ruby>myDict = { "hello" => 13, "world" => 31, "!" => 71 }

iterating over key-value pairs:

myDict.each {|key, value| puts "key = #{key}, value = #{value}"}

or

myDict.each_pair {|key, value| puts "key = #{key}, value = #{value}"}

iterating over keys:

myDict.each_key {|key| puts "key = #{key}"}

iterating over values:

myDict.each_value {|value| puts "value =#{value}"}</lang>

another way: <lang ruby>for key, value in myDict

 puts "key = #{key}, value = #{value}"

end

for key in myDict.keys

 puts "key = #{key}"

end

for value in myDict.values

 puts "value = #{value}"

end</lang>

Output:

key = hello, value = 13
key = world, value = 31
key = !, value = 71
key = hello
key = world
key = !
value = 13
value = 31
value = 71

Rust

<lang Rust>use std::collections::HashMap; fn main() {

 let mut squares = HashMap::new();
 squares.insert("one", 1i32);
 squares.insert("two", 4);
 squares.insert("three", 9);
 for key in squares.keys() {
   println!("Key {}", key);
 }
 for value in squares.values() {
   println!("Value {}", value);
 }
 for (key, value) in squares.iter() {
   println!("{} => {}", key, value);
 }

}</lang>

Scala

<lang Scala>val m = Map("Amsterdam" -> "Netherlands", "New York" -> "USA", "Heemstede" -> "Netherlands")

println(f"Key->Value: ${m.mkString(", ")}%s") println(f"Pairs: ${m.toList.mkString(", ")}%s") println(f"Keys: ${m.keys.mkString(", ")}%s") println(f"Values: ${m.values.mkString(", ")}%s")

println(f"Unique values: ${m.values.toSet.mkString(", ")}%s")</lang>

Output:


Key->Value: Amsterdam -> Netherlands, New York -> USA, Heemstede -> Netherlands
Pairs: (Amsterdam,Netherlands), (New York,USA), (Heemstede,Netherlands)
Keys: Amsterdam, New York, Heemstede
Values: Netherlands, USA, Netherlands
Unique values: Netherlands, USA

Scheme

Works with: Gauche Scheme

Create an associative array (hash-table) whose keys are strings

(define table (hash-table 'string=?

 '("hello" . 0) '("world" . 22) '("!" . 999)))

Iterate over the table, passing the key and the value of each entry as arguments to a function

(hash-table-for-each

 table
 ;; Create by "partial application" a function that accepts 2 arguments,
 ;; the key and the value:
 (pa$ format #t "Key = ~a, Value = ~a\n"))</lang>

Output:

Key = !, Value = 999
Key = world, Value = 22
Key = hello, Value = 0

Iterate over the table and create a list of the keys and the altered values

(hash-table-map

 table
 (lambda (key val) (list key (+ val 5000))))

Create a new table that has the same keys but altered values.

(use gauche.collection) (map-to <hash-table>

 (lambda (k-v) (cons (car k-v) (+ (cdr k-v) 5000)))
 table)

</lang>

To get a list of the keys or of the values of the table, use one of the following:

(hash-table-keys table)
(hash-table-values table)

Seed7

<lang seed7>$ include "seed7_05.s7i";

const type: dictType is hash [string] integer; var dictType: myDict is dictType.value;

const proc: main is func

 local
   var string: stri is "";
   var integer: number is 0;
 begin
   myDict @:= ["hello"] 1;
   myDict @:= ["world"] 2;
   myDict @:= ["!"] 3;

   # iterating over key-value pairs:
   for number key stri range myDict do
     writeln("key = " <& number <& ", value = " <& stri);
   end for;

   # iterating over keys:
   for key stri range myDict do
     writeln("key = " <& stri);
   end for;

   # iterating over values:
   for number range myDict do
     writeln("value = " <& number);
   end for;
 end func;</lang>

Output:

key = 3, value = !
key = 1, value = hello
key = 2, value = world
key = !
key = hello
key = world
value = 3
value = 1
value = 2

Sidef

<lang ruby>var hash = Hash.new(

   key1 => 'value1',
   key2 => 'value2',

);

Iterate over key-value pairs

hash.each { |key, value|

   say "#{key}: #{value}";

};

Iterate only over keys

hash.keys.each { |key|

   say key;

};

Iterate only over values

hash.values.each { |value|

   say value;

};</lang>

Output:

key1: value1
key2: value2
key1
key2
value1
value2

Slate

In Slate, all associative mappings inherit from Mapping, so they all have the same protocol. Even Sequences obey it, in addition to their own protocol for collections with ordered integer-range keys. <lang slate>define: #pairs -> ({'hello' -> 1. 'world' -> 2. '!' -> 3. 'another!' -> 3} as: Dictionary). pairs keysAndValuesDo: [| :key :value |

 inform: '(k, v) = (' ; key printString ; ', ' ; value printString ; ')'

].

pairs keysDo: [| :key |

 inform: '(k, v) = (' ; key printString ; ', ' ; (pairs at: key) printString ; ')'

].

pairs do: [| :value |

 inform: 'value = ' ; value printString

].</lang>

Smalltalk

Works with: GNU Smalltalk

<lang smalltalk>|pairs| pairs := Dictionary from: { 'hello' -> 1. 'world' -> 2. '!' -> 3. 'another!' -> 3 }.

"iterate over keys and values" pairs keysAndValuesDo: [ :k :v |

   ('(k, v) = (%1, %2)' % { k. v }) displayNl

].

"iterate over keys" pairs keysDo: [ :key |

   ('key = %1, value = %2' % { key. pairs at: key }) displayNl

].

"iterate over values" pairs do: [ :value |

   ('value = %1' % { value }) displayNl

].</lang>

We could also obtain a set of keys or a collection of values and iterate over them with "do:":

<lang smalltalk>(pairs keys) do: [ :k | "..." ]. (pairs values) do: [ :v | "..." ].</lang>

SNOBOL4

Works with: Macro Spitbol

Works with: Snobol4+

Works with: CSnobol

<lang SNOBOL4>* # Create sample table

       t = table()
       t<'cat'> = 'meow'
       t<'dog'> = 'woof'
       t<'pig'> = 'oink'

# Convert table to key/value array

       a = convert(t,'array')

# Iterate pairs

ploop i = i + 1; output = a<i,1> ' -> ' a<i,2> :s(ploop)

# Iterate keys

kloop j = j + 1; output = a<j,1> :s(kloop)

# Iterate vals

vloop k = k + 1; output = a<k,2> :s(vloop) end</lang>

Swift

<lang swift>let myMap = [ "hello": 13, "world": 31, "!" : 71 ]

// iterating over key-value pairs: for (key, value) in myMap {

   println("key = \(key), value = \(value)")

}</lang>

Tcl

With Arrays

<lang tcl>array set myAry {

   # list items here...

}

Iterate over keys and values

foreach {key value} [array get myAry] {

   puts "$key -> $value"

}

Iterate over just keys

foreach key [array names myAry] {

   puts "key = $key"

}

There is nothing for directly iterating over just the values
Use the keys+values version and ignore the keys</lang>

With Dictionaries

Works with: Tcl version 8.5

<lang tcl>set myDict [dict create ...]; # Make the dictionary

Iterate over keys and values

dict for {key value} $myDict {

   puts "$key -> $value"

}

Iterate over keys

foreach key [dict keys $myDict] {

   puts "key = $key"

}

Iterate over values

foreach value [dict values $myDict] {

   puts "value = $value"

}</lang>

TXR

<lang txr> @(do (defvar *h* (make-hash nil nil nil))

    (each ((k '(a b c))
           (v '(1 2 3)))
      (set [*h* k nil] v))
    (dohash (k v *h*)
      (format t "~a -> ~a\n" k v))))</lang>

$ txr hash.txr 
c -> 3
b -> 2
a -> 1

UNIX Shell

Two shells have associative arrays, but they use different syntax to access their keys.

Works with: ksh93

<lang bash>typeset -A a=([key1]=value1 [key2]=value2)

just keys

printf '%s\n' "${!a[@]}"

just values

printf '%s\n' "${a[@]}"

keys and values

for key in "${!a[@]}"; do printf '%s => %s\n' "$key" "${a[$key]}" done</lang>

Works with: zsh

<lang bash>typeset -A a a=(key1 value1 key2 value2)

just keys

print -l -- ${(k)a}

just values

print -l -- ${(v)a}

keys and values

printf '%s => %s\n' ${(kv)a}</lang>

Vala

Library: Gee

<lang vala> using Gee;

void main(){

   // declare HashMap                                                          
   var map = new HashMap<string, double?>();

   // set 3 entries                                                            
   map["pi"] = 3.14;
   map["e"] = 2.72;
   map["golden"] = 1.62;

   // iterate over (key,value) pair                                            
   foreach (var elem in map.entries){
       string name = elem.key;
       double num = elem.value;

stdout.printf("%s,%f\n", name, num);

   // iterate over keys                                                        
   foreach (string key in map.keys){

stdout.printf("%s\n", key);

   // iterate over values                                                      
   foreach (double num in map.values){

stdout.printf("%f\n", num);

} </lang>

Compile with flag:

--pkg gee-1.0

Output:

e,2.720000
golden,1.620000
pi,3.140000
e
golden
pi
2.720000
1.620000
3.140000

VBScript

<lang vb> 'instantiate the dictionary object Set dict = CreateObject("Scripting.Dictionary")

'populate the dictionary or hash table dict.Add 1,"larry" dict.Add 2,"curly" dict.Add 3,"moe"

'iterate key and value pairs For Each key In dict.Keys WScript.StdOut.WriteLine key & " - " & dict.Item(key) Next </lang>

Output:

1 - larry
2 - curly
3 - moe

Vim Script

<lang vim>let dict = {"apples": 11, "oranges": 25, "pears": 4}

echo "Iterating over key-value pairs" for [key, value] in items(dict)

   echo key " => " value

endfor echo "\n"

echo "Iterating over keys" for key in keys(dict)

   echo key

endfor echo "\n"

echo "Iterating over values" for value in values(dict)

   echo value

endfor</lang>

Output:

Iterating over key-value pairs                                                  
oranges  =>  25                                                                 
pears  =>  4                                                                    
apples  =>  11                                                                  
                                                                                
Iterating over keys                                                             
oranges                                                                         
pears                                                                           
apples                                                                          
                                                                                
Iterating over values                                                           
25                                                                              
4                                                                               
11

Wart

<lang wart>h <- (table 'a 1 'b 2) each (key val) table

 prn key " " val</lang>

Output:

a 1
b 2

XPL0

<lang XPL0>include c:\cxpl\stdlib; char Dict(10,10); int Entries;

proc AddEntry(Letter, Greek); \Insert entry into associative array char Letter, Greek; [Dict(Entries,0):= Letter; StrCopy(Greek, @Dict(Entries,1)); Entries:= Entries+1; \(limit checks ignored for simplicity) ];

int I; [Entries:= 0; AddEntry(^A, "alpha"); AddEntry(^D, "delta"); AddEntry(^B, "beta"); AddEntry(^C, "gamma"); for I:= 0 to Entries-1 do

   [ChOut(0, Dict(I,0));  ChOut(0, ^ );  Text(0, @Dict(I,1));  CrLf(0)];

]</lang>

Output:

A alpha
D delta
B beta
C gamma

zkl

<lang zkl>var d=D("A","alpha","D","delta", "B","beta", "C", "gamma"); d.keys.pump(Console.print,fcn(k){String(k,",")}) d.values.apply("toUpper").println(); d.makeReadOnly(); // can only iterate over k,v pairs if read only foreach k,v in (d){print(k,":",v,"; ")}</lang>

Output:

A,B,C,D,
L("ALPHA","BETA","GAMMA","DELTA")
A:alpha; B:beta; C:gamma; D:delta;