Associative array/Iteration

From Rosetta Code
Task
Associative array/Iteration
You are encouraged to solve this task according to the task description, using any language you may know.

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



Ada[edit]

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;
Output:
! 3
hello 1
world 2

ALGOL 68[edit]

Algol 68 does not have associative arrays as standard.
This sample defines a simple hash-based implementation with operators to iterate over the array.

# 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; # // #
 
# 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
Output:
  (2j)[2j value]
  (k1)[new k1 value]
  (k2)[k2 value]
  (z2)[z2 value]

Aime[edit]

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));
}
Output:
key A, value 33 (integer)
key B, value associative (text)
key C, value 2.5 (real)

App Inventor[edit]

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[edit]

Works with: AutoHotkey_L
From the documentation
; 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

AWK[edit]

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

BEGIN {
a["hello"] = 1
a["world"] = 2
a["!"] = 3
 
# iterate over keys
for(key in a) {
print key, a[key]
}
}

Babel[edit]

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

births (('Washington' 1732) ('Lincoln' 1809) ('Roosevelt' 1882) ('Kennedy' 1917)) ls2map ! <

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:

births cp dup {1 +} overmap !

To see the results, use the valmap operator:

valmap ! lsnum !
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:

births ('Roosevelt' 'Kennedy') lumapls ! lsnum !
Output:
( 1882 1917 )

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

births map2ls !

To view the list:

{give swap << " " << itod << "\n" <<} each
Output:
Kennedy 1917
Washington 1732
Roosevelt 1882
Lincoln 1809

To merge two maps together, use the mapmerge utility:

foo (("bar" 17) ("baz" 42)) ls2map ! <
births foo mergemap !

To view the results:

births map2ls ! {give swap << " " << itod << "\n" <<} each
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").

BASIC256[edit]

Solution is at Associative_array/Creation#BASIC256.

BBC BASIC[edit]

      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%

Bracmat[edit]

(  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
)
);
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[edit]

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}"
}

C[edit]

Solution is at Associative arrays/Creation/C.

C++[edit]

Works with: C++11
#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;
}


Pre C++11:

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;
}

C#[edit]

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());
}
}
}
}
 

Ceylon[edit]

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``");
}
 
}

Chapel[edit]

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);
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[edit]

 
(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))
 

CoffeeScript[edit]

hash =
a: 'one'
b: 'two'
 
for key, value of hash
console.log key, value
 
for key of hash
console.log key
 

Common Lisp[edit]

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

With association lists (alists)[edit]

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.

;; 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))

With property lists (plists)[edit]

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.

(loop for (key value) on plist :by 'cddr
do (format t "~&Key: ~a, Value: ~a." key value))

With hash tables[edit]

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.

(maphash (lambda (key value)
(format t "~&Key: ~a, Value: ~a." key value))
hash-table)

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

(loop for key being each hash-key of hash-table using (hash-value value)
do (format t "~&Key: ~a, Value: ~a." key value))

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.

(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)))))

D[edit]

Works with: D version 2
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);
}

Dao[edit]

 
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 )
}
 

Delphi[edit]

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.

E[edit]

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 (_).

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 .`)
}

EchoLisp[edit]

 
(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
 

Elena[edit]

#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 ].
].

Elixir[edit]

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)
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[edit]

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

F#[edit]

Iterating over both.

 
let myMap = [ ("Hello", 1); ("World", 2); ("!", 3) ]
 
for k, v in myMap do
printfn "%s -> %d" k v
 

Iterating over either keys or values only can be achieved through use of the _ wildcard token.

 
// Only prints the keys.
for k, _ in myMap do
printfn "%s" k
 
// Only prints the values.
for _, v in myMap do
printfn "%d" v
 

Factor[edit]

H{ { "hi" "there" } { "a" "b" } } [ ": " glue print ] assoc-each

There's also assoc-map, assoc-find, assoc-filter and many more.

Fantom[edit]

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

 
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")
}
}
}
 

Forth[edit]

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
 
\ 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
 
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[edit]

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)
}

Groovy[edit]

Solution:

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 }
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[edit]

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

Haskell[edit]

with Data.Map:

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

Icon and Unicon[edit]

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
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[edit]

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
nl__example 0
Values
get__example each nl__example 0
Both keys and values
(,&< get__example) each nl__example 0

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

Java[edit]

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);
}

Java 8 version

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

JavaScript[edit]

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.

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]);
});

Jq[edit]

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.

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]
 

Julia[edit]

Translation of: Python
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
Output:
key = !, value = 71
key = hello, value = 13
key = world, value = 31
key = !
key = hello
key = world
value = 71
value = 13
value = 31

K[edit]

Creating a dictionary.

   d: .((`"hello";1); (`"world";2);(`"!";3))

The keys are available via "!".

   !d
`hello `world `"!"
 
$!d / convert keys (symbols) as strings
("hello"
"world"
,"!")

Print the key value pairs.

   `0:{,/$x,": ",d[x]}'!d
hello: 1
world: 2
!: 3

The values are available via "[]".

   d[]
1 2 3
 
{x+1}'d[]
2 3 4

Lang5[edit]

: 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

Lasso[edit]

 
//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
 

LFE[edit]

Keys and Values[edit]

 
(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))
 

Just Keys[edit]

 
(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)))
 

Liberty BASIC[edit]

Needs the sublist library from http://basic.wikispaces.com/SubList+Library since LB does not have built-in associative arrays.

 
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
 
 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

LiveCode[edit]

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

Output

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

Lua[edit]

local t = {
["foo"] = "bar",
["baz"] = 6,
fortytwo = 7
}
 
for key,val in pairs(t) do
print(string.format("%s: %s", key, val))
end
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[edit]

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)
')
Output:
key-value pairs
`wow',`flame'
`bow',`7'

keys
`wow'
`bow'

values
`flame'
`7'

Maple[edit]

Iterate through indices when indices are all simple expressions:

 
> T := table( [ "A" = 1, "B" = 2, "C" = 3, "D" = 4 ] );
> for i in indices( T, nolist ) do print(i ) end:
"A"
 
"B"
 
"C"
 
"D"
 

Iterate through indices when indices may be expression sequences:

 
> 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
 

Return all index / entry pairs as equations:

 
> for i in indices( T, pairs ) do print( i) end:
"a" = 1
 
"b" = 2
 
("c", "d") = 3
 
 
> for i in entries( T ) do print( i) end:
[1]
 
[3]
 
[2]
 

Mathematica / Wolfram Language[edit]

keys=DownValues[#,Sort->False][[All,1,1,1]]&;
[email protected][#]&;
 
a[2]="string";a["sometext"]=23;
keys[a]
->{2,sometext}
hashes[a]
->{string,23}

MATLAB / Octave[edit]

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

   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;

or

   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;

Maxima[edit]

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))$

NetRexx[edit]

/* 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

NewLISP[edit]

;; 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))))

Nim[edit]

 
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
 
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[edit]

Works with: oo2c Version 2
 
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.
 

Objeck[edit]

 
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();
};
}
}
 

Objective-C[edit]

Works with: Objective-C version 2.0+
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);
}
Works with: Objective-C version <2.0
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);
}
Works with: Cocoa version Mac OS X 10.6+
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);
}];

OCaml[edit]

Association array:

#!/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 ;;

Hash table:

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" ;;

Functional binary search tree:

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" ;;

ooRexx[edit]

 
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
 

Oz[edit]

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

PARI/GP[edit]

Works with: PARI/GP version 2.8.1+

The keys can be retried from a map with Vec:

keys = Vec(M);

You can iterate over the values as usual:

for(i=1,#keys,
print(keys[i]," ",mapget(M,keys[i]))
)

Perl[edit]

#! /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";
}

Perl 6[edit]

Works with: Rakudo version 2015.12
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;

PHP[edit]

<?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";
}
?>

PicoLisp[edit]

Using properties[edit]

(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)

Using an index tree[edit]

(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)

Pike[edit]

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

 
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
 
 

PostScript[edit]

 
% 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
 

PowerShell[edit]

Using the following hash table:

$h = @{ 'a' = 1; 'b' = 2; 'c' = 3 }

Iterating over the key/value pairs is slightly cumbersome as it requires an explicit call to GetEnumerator:

$h.GetEnumerator() | ForEach-Object { Write-Host Key: $_.Name, Value: $_.Value }

A foreach statement can also be used:

foreach ($e in $h.GetEnumerator()) {
Write-Host Key: $e.Name, Value: $e.Value
}

Iterating over the keys:

$h.Keys | ForEach-Object { Write-Host Key: $_ }
 
foreach ($k in $h.Keys) {
Write-Host Key: $k
}

Iterating over the values:

$h.Values | ForEach-Object { Write-Host Value: $_ }
 
foreach ($v in $h.Values) {
Write-Host Value: $v
}

Prolog[edit]

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):

 
assert( mymap(key1,value1) ).
assert( mymap(key2,value1) ).
 

To perform the specific task at hand:

 
?- forall( mymap(Key,Value), writeln( [Key,Value]) ).
 
[key1,value1]
[key2,value1]
 

In Prolog, however, iteration is "built-in". For example:

 
?- mymap(key1, Y).
Y = value1.
 
?- mymap(X, value1).
X = key1 ;
X = key2.
 

To construct the list of keys:

 
?- findall( X, mymap(X,value1), Xs).
Xs = [key1, key2].
 

To construct the list of distinct values:

 
?- findall( Y, mymap(key1,Y), Ys).
Ys = [value1].
 

PureBasic[edit]

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

NewMap dict.s()
dict("de") = "German"
dict("en") = "English"
dict("fr") = "French"
 
ForEach dict()
Debug MapKey(dict()) + ":" + dict()
Next

Python[edit]

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)

R[edit]

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

environment example[edit]

> env <- new.env()
> env[["x"]] <- 123
> env[["x"]]
[1] 123
> index <- "1"
> env[[index]] <- "rainfed hay"
> for (name in ls(env)) {
+ cat(sprintf('index=%s, value=%s\n', name, env[[name]]))
+ }
index=1, value=rainfed hay
index=x, value=123

vector example[edit]

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

list example[edit]

> a <- list(a=1, b=2, c=3.14, d="xyz")
> print(a$a)
[1] 1
> print(a$d)
[1] "xyz"

Racket[edit]

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))
 

REXX[edit]

/*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 capitols.*/
stateN.=' [not defined yet] ' /*sets any/all state names. */
 
stateL= /*╔════════════════════════════════════════════════════════════════════╗
║ The list of states (empty now). It's convenient to have them in ║
║ alphabetic order; they'll be listed in this order. With a little ║
║ more code, they could be sorted quite easily. ║
║ ║
║ 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, ···).║
╚════════════════════════════════════════════════════════════════════╝*/

 
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', "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 capitols that were defined. */
q=word(stateL, j) /*get the next (USA) state in the list.*/
say 'the former capitol of ('q") " stateN.q " was " stateC.q
end /*j*/ /* [↑] show states that were defined.*/
exit /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
setSC: arg code; parse arg ,name,cap /*get uppercase code; get name &capitol*/
stateL=stateL code /*keep a list of all the US state codes*/
stateN.code=name /*set (define) the state's name. */
stateC.code=cap /* " " " " capitol. */
return /*return to invoker, SETSC is finished.*/

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[edit]

Associative arrays are called lists in 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
}
 
 
 

Ruby[edit]

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}"}

another way:

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

Rust[edit]

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);
 
}
}
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[edit]

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")
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[edit]

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"))

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)
 

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[edit]

$ 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;
Output:
key = 3, value = !
key = 1, value = hello
key = 2, value = world
key = !
key = hello
key = world
value = 3
value = 1
value = 2

Sidef[edit]

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;
}
Output:
key1: value1
key2: value2
key1
key2
value1
value2

Slate[edit]

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.

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
].

Smalltalk[edit]

Works with: GNU 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
].

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

(pairs keys) do: [ :k | "..." ].
(pairs values) do: [ :v | "..." ].

SNOBOL4[edit]

Works with: Macro Spitbol
Works with: Snobol4+
Works with: CSnobol
*       # 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

Swift[edit]

let myMap = [
"hello": 13,
"world": 31,
"!"  : 71 ]
 
// iterating over key-value pairs:
for (key, value) in myMap {
println("key = \(key), value = \(value)")
}

Tcl[edit]

With Arrays[edit]

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

With Dictionaries[edit]

Works with: Tcl version 8.5
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"
}

TXR[edit]

(defvarl h (hash))
 
(each ((k '(a b c))
(v '(1 2 3)))
(set [h k] v))
 
(dohash (k v h)
(put-line [email protected] -> @v`))
Run:
$ txr hash.tl 
c -> 3
b -> 2
a -> 1

UNIX Shell[edit]

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

Works with: ksh93
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
Works with: zsh
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}

Vala[edit]

Library: Gee
 
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);
}
}
 

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[edit]

 
'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
 
Output:
1 - larry
2 - curly
3 - moe

Vim Script[edit]

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
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[edit]

h <- (table 'a 1 'b 2)
each (key val) table
prn key " " val
Output:
a 1
b 2

XPL0[edit]

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)];
]
Output:
A alpha
D delta
B beta
C gamma

zkl[edit]

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