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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

11l

<lang 11l>V d = [‘key1’ = ‘value1’, ‘key2’ = ‘value2’]

L(key, value) d

  print(key‘ = ’value)

L(key) d.keys()

  print(key)

L(value) d.values()

  print(value)</lang>

Output:

key1 = value1
key2 = value2
key1
key2
value1
value2

8th

Iterating key,value pairs uses "m:each": <lang Forth> {"one": 1, "two": "bad"} ( swap . space . cr ) m:each </lang>

Output:

one 1 two bad

Iterating the keys uses "m:keys": <lang Forth> {"one": 1, "two": "bad"} m:keys ( . cr ) a:each </lang>

Output:

one two

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

Algol 68 does not have associative arrays as standard.
This sample defines a simple hash-based implementation with operators to iterate over the array. <lang algol68># associative array handling using hashing #

the modes allowed as associative array element values - change to suit #

MODE AAVALUE = STRING;

the modes allowed as associative array element keys - change to suit #

MODE AAKEY = STRING;

nil element value #

REF AAVALUE nil value = NIL;

an element of an associative array #

MODE AAELEMENT = STRUCT( AAKEY key, REF AAVALUE value );

a list of associative array elements - the element values with a #
particular hash value are stored in an AAELEMENTLIST #

MODE AAELEMENTLIST = STRUCT( AAELEMENT element, REF AAELEMENTLIST next );

nil element list reference #

REF AAELEMENTLIST nil element list = NIL;

nil element reference #

REF AAELEMENT nil element = NIL;

the hash modulus for the associative arrays #

INT hash modulus = 256;

generates a hash value from an AAKEY - change to suit #

OP HASH = ( STRING key )INT: BEGIN

   INT result := ABS ( UPB key - LWB key ) MOD hash modulus;
   FOR char pos FROM LWB key TO UPB key DO
       result PLUSAB ( ABS key[ char pos ] - ABS " " );
       result MODAB  hash modulus
   OD;
   result

END; # HASH #

a mode representing an associative array #

MODE AARRAY = STRUCT( [ 0 : hash modulus - 1 ]REF AAELEMENTLIST elements

                   , INT                                       curr hash
                   , REF AAELEMENTLIST                         curr position
                   );

initialises an associative array so all the hash chains are empty #

OP INIT = ( REF AARRAY array )REF AARRAY:

    BEGIN
        FOR hash value FROM 0 TO hash modulus - 1 DO ( elements OF array )[ hash value ] := nil element list OD;
        array
    END; # INIT #

gets a reference to the value corresponding to a particular key in an #
associative array - the element is created if it doesn't exist #

PRIO // = 1; OP // = ( REF AARRAY array, AAKEY key )REF AAVALUE: BEGIN

   REF AAVALUE result;
   INT         hash value = HASH key;
   # get the hash chain for the key #
   REF AAELEMENTLIST element := ( elements OF array )[ hash value ];
   # find the element in the list, if it is there #
   BOOL found element := FALSE;
   WHILE ( element ISNT nil element list )
     AND NOT found element
   DO
       found element := ( key OF element OF element = key );
       IF found element
       THEN
           result  := value OF element OF element
       ELSE
           element := next OF element
       FI
   OD;
   IF NOT found element
   THEN
       # the element is not in the list #
       # - add it to the front of the hash chain #
       ( elements OF array )[ hash value ]
                           := HEAP AAELEMENTLIST
                           := ( HEAP AAELEMENT := ( key
                                                  , HEAP AAVALUE := ""
                                                  )
                              , ( elements OF array )[ hash value ]
                              );
       result := value OF element OF ( elements OF array )[ hash value ]
   FI;
   result

END; # // #

returns TRUE if array contains key, FALSE otherwise #

PRIO CONTAINSKEY = 1; OP CONTAINSKEY = ( REF AARRAY array, AAKEY key )BOOL: BEGIN

   # get the hash chain for the key #
   REF AAELEMENTLIST element := ( elements OF array )[ HASH key ];
   # find the element in the list, if it is there #
   BOOL found element := FALSE;
   WHILE ( element ISNT nil element list )
     AND NOT found element
   DO
       found element := ( key OF element OF element = key );
       IF NOT found element
       THEN
           element := next OF element
       FI
   OD;
   found element

END; # CONTAINSKEY #

gets the first element (key, value) from the array #

OP FIRST = ( REF AARRAY array )REF AAELEMENT: BEGIN

   curr hash     OF array := LWB ( elements OF array ) - 1;
   curr position OF array := nil element list;
   NEXT array

END; # FIRST #

gets the next element (key, value) from the array #

OP NEXT = ( REF AARRAY array )REF AAELEMENT: BEGIN

   WHILE ( curr position OF array IS nil element list )
     AND   curr hash     OF array < UPB ( elements OF array )
   DO
       # reached the end of the current element list - try the next         #
       curr hash     OF array +:= 1;
       curr position OF array  := ( elements OF array )[ curr hash OF array ]
   OD;
   IF   curr hash OF array > UPB ( elements OF array )
   THEN
       # no more elements #
       nil element
   ELIF curr position OF array IS nil element list
   THEN
       # reached the end of the table #
       nil element
   ELSE
       # have another element #
       REF AAELEMENTLIST found element = curr position OF array;
       curr position OF array := next OF curr position OF array;
       element OF found element
   FI

END; # NEXT #

test the associative array #

BEGIN

   # create an array and add some values  #
   REF AARRAY a1 := INIT LOC AARRAY;
   a1 // "k1" := "k1 value";
   a1 // "z2" := "z2 value";
   a1 // "k1" := "new k1 value";
   a1 // "k2" := "k2 value";
   a1 // "2j" := "2j value";
   # iterate over the values #
   REF AAELEMENT e := FIRST a1;
   WHILE e ISNT nil element
   DO
       print( ( "  (" + key OF e + ")[" + value OF e + "]", newline ) );
       e := NEXT a1
   OD

END</lang>

Output:

  (2j)[2j value]
  (k1)[new k1 value]
  (k2)[k2 value]
  (z2)[z2 value]

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 (rsk_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>

Arturo

<lang arturo>// create a dictionary dict: #{ name: "john" surname: "doe" age: 33 }

// Iterate over key/value pairs loop dict { print "key = " + &0 + ", value = " + &1 }

print "----"

// Iterate over keys loop [keys dict] { print "key = " + & }

print "----"

// Iterate over values loop [values dict] { print "value = " + & }</lang>

Output:

key = surname, value = doe
key = age, value = 33
key = name, value = john
----
key = surname
key = age
key = name
----
value = doe
value = 33
value = john

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

In Babel, associative arrays are referred to as maps. To create a map from a list-of-lists:

<lang babel>births (('Washington' 1732) ('Lincoln' 1809) ('Roosevelt' 1882) ('Kennedy' 1917)) ls2map ! <</lang>

To iterate over a map, in the primary sense, use the overmap utility. We will copy the map (cp operator) so as not to modify the original:

<lang babel>births cp dup {1 +} overmap !</lang>

To see the results, use the valmap operator:

<lang babel>valmap ! lsnum !</lang>

Output:

( 1918 1733 1883 1810 )

There are many ways to interact with a map in Babel. Most of these begin by converting the map to a list or list-of-lists. To look up a list of specific values from the map, by key, use the lumapls utility:

<lang babel>births ('Roosevelt' 'Kennedy') lumapls ! lsnum !</lang>

Output:

( 1882 1917 )

To convert the entire map back to a list of key-value pairs:

<lang babel>births map2ls !</lang>

To view the list:

Output:

Kennedy 1917
Washington 1732
Roosevelt 1882
Lincoln 1809

To merge two maps together, use the mapmerge utility:

To view the results:

<lang babel>births map2ls ! {give swap << " " << itod << "\n" <<} each</lang>

Output:

baz 42
Kennedy 1917
bar 17
Washington 1732
Roosevelt 1882
Lincoln 1809

For more information on maps in Babel, view std.sp (see the section titled "map utilities").

BaCon

<lang qbasic>DECLARE associative ASSOC STRING

associative("abc") = "first three" associative("mn") = "middle two" associative("xyz") = "last three"

LOOKUP associative TO keys$ SIZE amount FOR i = 0 TO amount - 1

   PRINT keys$[i], ":", associative(keys$[i])

NEXT</lang>

Output:

prompt$ ./assoc
abc:first three
mn:middle two
xyz:last three

LOOKUP creates a numerically indexed array of the keys of the associative array, with the number of elements stored in the field following the SIZE keyword.

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>

Ceylon

<lang ceylon>shared void run() {

value myMap = map { "foo" -> 5, "bar" -> 10, "baz" -> 15 };

for(key in myMap.keys) { print(key); }

for(item in myMap.items) { print(item); }

for(key->item in myMap) { print("``key`` maps to ``item``"); }

}</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>

Alternate solution

I use Allegro CL 10.1

Project

Associative array/Iteration

(setf x (make-array '(3 2)

          :initial-contents '(("hello" 13 ) ("world" 31) ("!" 71))))

(setf xlen (array-dimensions x)) (setf len (car xlen)) (dotimes (n len)

              (terpri)
              (format t "~a" (aref x n 0))
              (format t "~a" " : ") 
              (format t "~a" (aref x n 1)))

</lang> Output:

hello : 13
world : 31
! : 71

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>

Dart

<lang javascript> main(){ var fruits = { 'apples': 'red', 'oranges': 'orange', 'bananas': 'yellow', 'pears': 'green', 'plums': 'purple' };

print('Key Value pairs:'); fruits.forEach( (fruits, color) => print( '$fruits are $color' ) );

print('\nKeys only:'); fruits.keys.forEach( ( key ) => print( key ) );

print('\nValues only:'); fruits.values.forEach( ( value ) => print( value ) ); } </lang>

Output:

Key Value pairs:
apples are red
oranges are orange
bananas are yellow
pears are green
plums are purple

Keys only:
apples
oranges
bananas
pears
plums

Values only:
red
orange
yellow
green
purple

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>

Dyalect

<lang dyalect>var t = (x: 1, y: 2, z: 3)

for x in t.keys() {

   print("\(x)=\(t[x])")

}</lang>

Output:

x=1
y=2
z=3

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>

EchoLisp

<lang scheme> (lib 'hash) ;; load hash.lib (define H (make-hash))

fill hash table

(hash-set H 'Simon 42) (hash-set H 'Albert 666) (hash-set H 'Antoinette 33)

iterate over (key . value ) pairs

(for ([kv H]) (writeln kv)) (Simon . 42) (Albert . 666) (Antoinette . 33)

iterate over keys

(for ([k (hash-keys H)]) (writeln 'key-> k)) key-> Simon key-> Albert key-> Antoinette

iterate over values

(for ([v (hash-values H)]) (writeln 'value-> v)) value-> 42 value-> 666 value-> 33 </lang>

Elena

ELENA 5.0 : <lang elena>import system'collections; import system'routines; import extensions;

public program() {

   // 1. Create
   var map := Dictionary.new();
   map["key"] := "foox";
   map["key"] := "foo";
   map["key2"]:= "foo2";
   map["key3"]:= "foo3";
   map["key4"]:= "foo4";

   // Enumerate
   map.forEach:
       (keyValue){ console.printLine(keyValue.Key," : ",keyValue.Value) }

}</lang>

Strong typed dictionary

<lang elena>import system'collections; import system'routines; import extensions;

public program() {

   // 1. Create
   auto map := new Map<string,string>();
   map["key"] := "foox";
   map["key"] := "foo";
   map["key2"]:= "foo2";
   map["key3"]:= "foo3";
   map["key4"]:= "foo4";

   // Enumerate
   map.forEach:
       (tuple){ console.printLine(tuple.Item1," : ",tuple.Item2) }

}</lang>

Elixir

<lang elixir>IO.inspect d = Map.new([foo: 1, bar: 2, baz: 3]) Enum.each(d, fn kv -> IO.inspect kv end) Enum.each(d, fn {k,v} -> IO.puts "#{inspect k} => #{v}" end) Enum.each(Map.keys(d), fn key -> IO.inspect key end) Enum.each(Map.values(d), fn value -> IO.inspect value end)</lang>

Output:

%{bar: 2, baz: 3, foo: 1}
{:bar, 2}
{:baz, 3}
{:foo, 1}
:bar => 2
:baz => 3
:foo => 1
:bar
:baz
:foo
2
3
1

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

Free Pascal

FPC 3.2.0+. Similar to Delphi:<lang pascal>program AssociativeArrayIteration; {$mode delphi}{$ifdef windows}{$apptype console}{$endif} uses Generics.Collections;

type

 TlDictionary =  TDictionary<string, Integer>;
 TlPair = TPair<string,integer>;

var

 i: Integer;
 s: string;
 lDictionary: TlDictionary;
 lPair: TlPair;

begin

 lDictionary := TlDictionary.Create;
 try
   lDictionary.Add('foo', 5);
   lDictionary.Add('bar', 10);
   lDictionary.Add('baz', 15);
   lDictionary.AddOrSetValue('foo',6);
   for lPair in lDictionary do
     Writeln('Pair: ',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>

Pair: foo = 6
Pair: bar = 10
Pair: baz = 15
Key: foo
Key: bar
Key: baz
Value: 6
Value: 10
Value: 15

Gambas

Click this link to run this code <lang gambas>Public Sub Main() Dim cList As Collection = ["2": "quick", "4": "fox", "1": "The", "9": "dog", "7": "the", "5": "jumped", "3": "brown", "6": "over", "8": "lazy"] Dim siCount As Short Dim sTemp As String

For Each sTemp In cList

 Print cList.key & "=" & sTemp;;

For siCount = 1 To cList.Count

 Print cList[Str(siCount)];;

2=quick 4=fox 1=The 9=dog 7=the 5=jumped 3=brown 6=over 8=lazy 
The quick brown fox jumped over the lazy dog

Go

Language: <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> Standard library templates:

In addition to the for/range features of the language, the text/template and html/template packages of the standard library have map iteration features. Some differences worth noting:

A single assigned value in a template is the map value. With the language for/range it is the key.
Templates have no equivalent of _; a dummy variable must be used.
In a template, if map keys are a comparable basic type, then iteration proceeds in key order. With the language for/range, iteration is in non-deterministic order.

<lang go>package main

import (

   "os"
   "text/template"

)

func main() {

   m := map[string]int{
       "hello": 13,
       "world": 31,
       "!":     71,
   }

   // iterating over key-value pairs:
   template.Must(template.New("").Parse(`

Template:- range $k, $v := . - key = Template:$k, value = Template:$v Template:End - `)).Execute(os.Stdout, m)

   // iterating over keys:
   template.Must(template.New("").Parse(`

Template:- range $k, $v := . - key = Template:$k Template:End - `)).Execute(os.Stdout, m)

   // iterating over values:
   template.Must(template.New("").Parse(`

Template:- range . - value = {{.}} Template:End - `)).Execute(os.Stdout, m) }</lang>

Output:

Note order by key.

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

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

main :: IO () main =

 (putStrLn . unlines) $
 [ show . M.toList     -- Pairs
 , show . M.keys       -- Keys
 , show . M.elems      -- Values
 ] <*>
 pure myMap</lang>

Output:

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

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

Io

<lang Io>myDict := Map with(

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

)

// iterating over key-value pairs: myDict foreach( key, value,

   writeln("key = ", key, ", value = ", value)

)

// iterating over keys: myDict keys foreach( key,

   writeln("key = ", key)

)

// iterating over values: myDict foreach( value,

   writeln("value = ", value)

) // or alternatively: myDict values foreach( value,

   writeln("value = ", value)

)</lang>

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

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

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

}

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

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

}

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

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

}</lang>

Java 8 version

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

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

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

});

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

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

Output:

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

Works with: Julia version 0.6

<lang julia>dict = Dict("hello" => 13, "world" => 31, "!" => 71)

applying a function to key-value pairs:

foreach(println, dict)

iterating over key-value pairs:

for (key, value) in dict

   println("dict[$key] = $value")

end

iterating over keys:

for key in keys(dict)

   @show key

end

iterating over values:

for value in values(dict)

   @show 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>

Kotlin

<lang scala>fun main(a: Array<String>) {

   val map = mapOf("hello" to 1, "world" to 2, "!" to 3)

   with(map) {
       entries.forEach { println("key = ${it.key}, value = ${it.value}") }
       keys.forEach { println("key = $it") }
       values.forEach { println("value = $it") }
   }

}</lang>

Output:

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

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

Lingo

<lang lingo>hash = [#key1:"value1", #key2:"value2", #key3:"value3"]

-- iterate over key-value pairs repeat with i = 1 to hash.count

 put hash.getPropAt(i) & "=" & hash[i]

end repeat

-- iterating over values only can be written shorter repeat with val in hash

 put val

end repeat</lang>

LiveCode

<lang LiveCode>put 3 into fruit["apples"] put 5 into fruit["pears"] put 6 into fruit["oranges"] put "none" into fruit["bananas"]

put "Keys:" & cr & the keys of fruit & cr into tTmp put "Values 1:" & tab after tTmp repeat for each line tKey in the keys of fruit

   put fruit[tkey] & comma after tTmp

end repeat

-- need to copy array as combine will change variable put fruit into fruit2 combine fruit2 using comma put cr & "Values2:" & tab after tTmp repeat for each item f2val in fruit2

   put f2val & comma after tTmp

end repeat

combine fruit using return and ":" put cr & "Key:Values" & cr & fruit after tTmp -- alternatively, use same loop as for values 1 with tkey && fruit[tKey]

put tTmp</lang> Output <lang LiveCode>Keys: apples pears oranges bananas Values 1: 3,5,6,none, Values2: 3,none,6,5, Key:Values apples:3 bananas:none oranges:6 pears:5</lang>

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.

M2000 Interpreter

<lang M2000 Interpreter> Module checkit {

     \\ Inventories are objects with keys and values, or keys (used as read only values)
     \\ They use hash function.
     \\ Function TwoKeys return Inventory object (as a pointer to object)
     Function TwoKeys {
           Inventory Alfa="key1":=100, "key2":=200
           =Alfa
     }
     M=TwoKeys()
     Print Type$(M)="Inventory"
     \\ Normal Use:
           \\ Inventories Keys are case sensitive
           \\ M2000 identifiers are not case sensitive
     Print M("key1"), m("key2")
     \\ numeric values can convert to strings
     Print M$("key1"), m$("key2")
     \\ Iteration
     N=Each(M)
     While N {
           Print Eval(N)  ' prints 100, 200 as number
           Print M(N^!)  ' The same using index N^
     }
     N=Each(M)
     While N {
           Print Eval$(N)  ' prints  100, 200 as strings
           Print M$(N^!)  ' The same using index N^
     }
     N=Each(M)
     While N {
           Print Eval$(N, N^)  ' Prints Keys
     }
     \\ double iteration
     Append M, "key3":=500
     N=Each(M, 1, -1)  ' start to end
     N1=Each(M, -1, 1) ' end to start
     \\ 3x3 prints
     While N {
           While N1 {
                 Print format$("{0}*{1}={2}", Eval(N1), Eval(N), Eval(N1)*Eval(N))
           }
     }
     \\ sort results from lower product to greater product (3+2+1, 6 prints only)
     N=Each(M, 1, -1)  
     While N {
           N1=Each(M, N^+1, -1) 
           While N1 {
                 Print format$("{0}*{1}={2}", Eval(N1), Eval(N), Eval(N1)*Eval(N))
           }
     }
     N=Each(M)
     N1=Each(M,-2, 1)  ' from second from end to start
     \\ print only 2 values. While block ends when one iterator finish
     While N, N1 {
           Print Eval(N1)*Eval(N)
     }

} Checkit </lang>

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 / Wolfram Language

<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>

MiniScript

<lang MiniScript>d = { 3: "test", "foo": 3 }

for keyVal in d

   print keyVal   // produces results like: { "key": 3, "value": "test" }

end for

for key in d.indexes

   print key

end for

for val in d.values

   print val

end for</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: Table[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>

Ol

create sample associative array

(define aa (list->ff '(

  (hello . 1)
  (world . 2)
  (! . 3))))

(print aa)

==> #((! . 3) (hello . 1) (world . 2))

simplest iteration over all associative array (using ff-iter, lazy iterator)

(let loop ((kv (ff-iter aa)))

  (cond
     ((null? kv) #true)
     ((pair? kv)
        (print (car kv))
        (loop (cdr kv)))
     (else (loop (force kv)))))

==> (! . 3)
==> (hello . 1)
==> (world . 2)

iteration with returning value (using ff-fold)

(print

  "folding result: "
  (ff-fold
     (lambda (result key value)
        (print "key: " key ", value: " value)
        (+ result 1))
     0
     aa))

==> key: !, value: 3
==> key: hello, value: 1
==> key: world, value: 2
==> folding result: 3

same but right fold (using ff-foldr)

(print

  "rfolding result: "
  (ff-foldr
     (lambda (result key value)
        (print "key: " key ", value: " value)
        (+ result 1))
     0
     aa))

==> key: world, value: 2
==> key: hello, value: 1
==> key: !, value: 3
==> rfolding result: 3

at least create new array from existing (let's multiply every value by value)

(define bb (ff-map aa

     (lambda (key value)
        (* value value))))

(print bb)

==> #((! . 9) (hello . 1) (world . 4))

</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>

Output:

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

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 2015.12

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

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

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

}

Stable order

for %pairs.sort(*.value)>>.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>

Phix

The first three lines create a simple dictionary, with keys and values of several different types (string/integer/sequence): <lang Phix>setd("one",1) setd(2,"duo") setd({3,4},{5,"six"})

function visitor(object key, object data, object /*userdata*/)

   ?{key,data}
   return 1    -- (continue traversal)

end function traverse_dict(routine_id("visitor"))</lang>

Output:

{2,"duo"}
{{3,4},{5,"six"}}
{"one",1}

You could also use some of the map.e routines. With the same initial three setd() as above: <lang Phix>include builtins\map.e ?pairs() ?keys() ?values()</lang>

Output:

{{2,"duo"},{{3,4},{5,"six"}},{"one",1}}
{2,{3,4},"one"}
{"duo",{5,"six"},1}

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>

Potion

We can traverse tables by key or by key and val. We cannot traverse tables only by val. <lang potion>mydictionary = (red=0xff0000, green=0x00ff00, blue=0x0000ff)

mydictionary each (key, val): (key, ":", val, "\n") join print. mydictionary each (key): (key, "\n") join print.</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 demonstrates how to set and 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 capitals.*/ stateN.= ' [not defined yet] ' /*sets any/all state names. */ w = 0 /*the maximum length of a state name.*/ stateL = /*╔════════════════════════════════════════════════════════════════════════════════════╗

 ║ The list of states (empty as of now).  It's convenient to have them in alphabetic  ║
 ║ order;  they'll be listed in the order as they are in the REXX program below).     ║
 ║ In REXX,  when a key is used  (for a stemmed array,  as they are called in REXX),  ║
 ║ and the key isn't assigned a value,  the key's  name  is stored (internally)  as   ║
 ║ uppercase  (Latin)  characters  (as in the examples below.   If the  key  has a    ║
 ║ a value, the key's value is used as is  (i.e.:  no upper translation is performed).║
 ║ Actually,  any characters can be used,  including blank(s)  and  non─displayable   ║
 ║ characters  (including   '00'x,   'ff'x,   commas,   periods,   quotes,   ···).    ║
 ╚════════════════════════════════════════════════════════════════════════════════════╝*/

call setSC 'al', "Alabama" , 'Tuscaloosa' call setSC 'ca', "California" , 'Benicia' call setSC 'co', "Colorado" , 'Denver City' call setSC 'ct', "Connecticut" , 'Hartford and New Haven (jointly)' 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', "Missouri" , '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 defined. */
      $= word(stateL, j)                        /*get the next (USA) state in the list.*/
      say 'the former capital of  ('$") "    left(stateN.$, w)      " was "      stateC.$
      end    /*j*/                              /* [↑]   show states that were defined.*/

exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ setSC: parse arg code,name,cap; upper code /*get code, name & cap.; uppercase code*/

      stateL= stateL code                       /*keep a list of all the US state codes*/
      stateN.code= name; w= max(w,length(name)) /*define the state's name;  max width. */
      stateC.code= cap                          /*   "    "     "   code to the capital*/
      return                                    /*return to invoker, SETSC is finished.*/</lang>

output when using the internal default input:

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  (jointly)
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)  Missouri        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 capital (Lancaster).

Ring

Project : Associative array/Iteration

lst = [["hello", 13], ["world", 31], ["!", 71]] for n = 1 to len(lst)

   see lst[n][1] + " : " + lst[n][2] + nl

next </lang> Output:

hello : 13
world : 31
! : 71

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>my_dict = { "hello" => 13, "world" => 31, "!" => 71 }

iterating over key-value pairs:

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

or

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

iterating over keys:

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

iterating over values:

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

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

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

end

for key in my_dict.keys

 puts "key = #{key}"

end

for value in my_dict.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 olympic_medals = HashMap::new();
   olympic_medals.insert("United States", (1072, 859, 749));
   olympic_medals.insert("Soviet Union", (473, 376, 355));
   olympic_medals.insert("Great Britain", (246, 276, 284));
   olympic_medals.insert("Germany", (252, 260, 270));
   for (country, medals) in olympic_medals {
       println!("{} has had {} gold medals, {} silver medals, and {} bronze medals", 
              country, medals.0, medals.1, medals.2);
           
   }

}</lang>

Output:

Note that HashMap does not preserve order (if this is important, std::collections::BTreeMap is what you want.)

Germany has had 252 gold medals, 260 silver medals, and 270 bronze medals
United States has had 1072 gold medals, 859 silver medals, and 749 bronze medals
Soviet Union has had 473 gold medals, 376 silver medals, and 355 bronze medals
Great Britain has had 246 gold medals, 276 silver medals, and 284 bronze medals

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>

Stata

<lang stata>mata // Create an associative array a=asarray_create() asarray(a,"one",1) asarray(a,"two",2)

// Loop over entries loc=asarray_first(a) do { printf("%s %f\n",asarray_key(a,loc),asarray_contents(a,loc)) loc=asarray_next(a,loc) } while(loc!=NULL) 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 txrlisp>(defvarl h (hash))

(each ((k '(a b c))

      (v '(1 2 3)))
 (set [h k] v))

(dohash (k v h)

 (put-line `@k -> @v`))</lang>

Run:

$ txr hash.tl 
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

VBA

Dictionaries are similar in VBA and VBScript. Here is how to iterate.

<lang vb>Option Explicit Sub Test()

   Dim h As Object, i As Long, u, v, s
   Set h = CreateObject("Scripting.Dictionary")
   h.Add "A", 1
   h.Add "B", 2
   h.Add "C", 3

   'Iterate on keys
   For Each s In h.Keys
       Debug.Print s
   Next

   'Iterate on values
   For Each s In h.Items
       Debug.Print s
   Next

   'Iterate on both keys and values by creating two arrays
   u = h.Keys
   v = h.Items
   For i = 0 To h.Count - 1
       Debug.Print u(i), v(i)
   Next

End Sub</lang>

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=Dictionary("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;