Loops/Foreach

From Rosetta Code
Jump to: navigation, search
Task
Loops/Foreach
You are encouraged to solve this task according to the task description, using any language you may know.

Loop through and print each element in a collection in order. Use your language's "for each" loop if it has one, otherwise iterate through the collection in order with some other loop.

Contents

[edit] ACL2

(defun print-list (xs)
(if (endp xs)
nil
(prog2$ (cw "~x0~%" (first xs))
(print-list (rest xs)))))
> (print-list (list 1 "a" 1/2 (list 1 2) 'sym))
1
"a"
1/2
(1 2)
SYM
NIL

[edit] Ada

[edit] arrays

with Ada.Integer_Text_IO;
use Ada.Integer_Text_IO;
 
procedure For_Each is
 
A : array (1..5) of Integer := (-1, 0, 1, 2, 3);
 
begin
 
for Num in A'Range loop
Put( A (Num) );
end loop;
 
end For_Each;

Alternative solution (Ada 2012):

   for Item of A loop
Put( Item );
end loop;

[edit] doubly linked lists

Works with: Ada 2005
with Ada.Integer_Text_IO, Ada.Containers.Doubly_Linked_Lists;
use Ada.Integer_Text_IO, Ada.Containers;
 
procedure Doubly_Linked_List is
 
package DL_List_Pkg is new Doubly_Linked_Lists (Integer);
use DL_List_Pkg;
 
procedure Print_Node (Position : Cursor) is
begin
Put (Element (Position));
end Print_Node;
 
DL_List : List;
 
begin
 
DL_List.Append (1);
DL_List.Append (2);
DL_List.Append (3);
 
-- Iterates through every node of the list.
DL_List.Iterate (Print_Node'Access);
 
end Doubly_Linked_List;

[edit] vectors

Works with: Ada 2005
with Ada.Integer_Text_IO, Ada.Containers.Vectors;
use Ada.Integer_Text_IO, Ada.Containers;
 
procedure Vector_Example is
 
package Vector_Pkg is new Vectors (Natural, Integer);
use Vector_Pkg;
 
procedure Print_Element (Position : Cursor) is
begin
Put (Element (Position));
end Print_Element;
 
V : Vector;
 
begin
 
V.Append (1);
V.Append (2);
V.Append (3);
 
-- Iterates through every element of the vector.
V.Iterate (Print_Element'Access);
 
end Vector_Example;

[edit] Aikido

Aikido's foreach loop allows iteration through multiple value types.

[edit] strings

var str = "hello world"
foreach ch str { // you can also use an optional 'in'
println (ch) // one character at a time
}

[edit] vectors

var vec = [1,2,3,4]
foreach v vec { // you can also use an optional 'in'
println (v)
}

[edit] maps

var cities = {"San Ramon": 50000, "Walnut Creek": 70000, "San Francisco": 700000}   // map literal
foreach city cities {
println (city.first + " has population " + city.second)
}

[edit] integers

foreach i 100 {
println (i) // prints values 0..99
}
 
foreach i 10..20 {
println (i) // prints values 10..20
}
 
var a = 20
var b = 10
foreach i a..b {
println (i) // prints values from a to b (20..10)
}

[edit] Objects

Aikido allows definition of a foreach operator for an object. In this example we define a single linked list and a foreach operator to iterate through it

class List {
class Element (public data) {
public var next = null
}
var start = null
 
public function insert (data) {
var element = new Element (data)
element.next = start
start = element
}
 
public operator foreach (var iter) {
if (typeof(iter) == "none") { // first iteration
iter = start
return iter.data
} elif (iter.next == null) { // check for last iteration
iter = none
} else {
iter = iter.next // somewhere in the middle
return iter.data
}
}
 
}
 
var list = new List()
list.insert (1)
list.insert (2)
list.insert (4)
 
foreach n list {
println (n)
}

[edit] Coroutines

Aikido supports coroutines. The foreach operator may be used to iterate thorough the generated values.

// coroutine to generate the squares of a sequence of numbers
function squares (start, end) {
for (var i = start ; i < end ; i++) {
yield i*i
}
}
 
var start = 10
var end = 20
 
foreach s squares (start, end) {
println (s)
}

[edit] Files

If you open a file you can iterate through all the lines

var s = openin ("input.txt")
foreach line s {
print (line)
}

[edit] Enumerations

enum Color { 
RED, GREEN, BLUE
}
 
foreach color Color {
println (color)
}

[edit] ALGOL 68

Works with: ALGOL 68 version Standard - no extensions to language used
Works with: ALGOL 68G version Any - tested with release mk15-0.8b.fc9.i386
Works with: ELLA ALGOL 68 version Any (with appropriate job cards) - tested with release 1.8.8d.fc9.i386
[]UNION(STRING, INT, PROC(REF FILE)VOID) collection = ("Mary","Had",1,"little","lamb.",new line);
 
FOR index FROM LWB collection TO UPB collection DO
print((collection[index]," "))
OD

Output:

Mary Had          +1 little lamb.

Note: ALGOL 68S actually has a reserved word FOREACH that is used to break arrays in to portions, and process in parallel.

[edit] AmigaE

PROC main()
DEF a_list : PTR TO LONG, a
a_list := [10, 12, 14]
FOR a := 0 TO ListLen(a_list)-1
WriteF('\d\n', a_list[a])
ENDFOR
-> if the "action" fits a single statement, we can do instead
ForAll({a}, a_list, `WriteF('\d\n', a))
ENDPROC

[edit] AutoHotkey

string = mary,had,a,little,lamb
Loop, Parse, string, `,
MsgBox %A_LoopField%

[edit] AWK

The for (element_index in array) can be used, but it does not give elements' indexes in the order inside the array (AWK indexes in array are indeed more like hashes).

 
BEGIN {
split("Mary had a little lamb", strs, " ")
for(el in strs) {
print strs[el]
}
}

If elements must be returned in some order, keys must be generated in that order. In the example above the array is filled through the split function, which uses indexes from 1. So to iterate over the array's elements in the right order, a normal loop can be used:

BEGIN {
n = split("Mary had a little lamb", strs, " ")
for(i=1; i <= n; i++) {
print strs[i]
}
}

Note that in awk, foreach loops can only be performed against an associative container. It is not possible to loop against an explicit list, so the following will not work:

# This will not work
BEGIN {
for (l in "apples","bananas","cherries") {
print "I like " l
}

[edit] BASIC256

BASIC-256 does not have a FOR EACH type statement. Use a FOR loop to iterate through an array by index.

DIM collection$(1)
collection$ = { "The", "quick", "brown", "fox", "jumps", "over", "the", "lazy", "dog." }
 
FOR i = 0 TO collection$[?]-1
PRINT collection$[i]+ " ";
NEXT i
PRINT

Output:

The quick brown fox jumps over the lazy dog.

[edit] BBC BASIC

      DIM collection$(8)
collection$() = "The", "quick", "brown", "fox", "jumps", \
\ "over", "the", "lazy", "dog."
 
FOR index% = 0 TO DIM(collection$(), 1)
PRINT collection$(index%) " ";
NEXT
PRINT

[edit] bc

There is no "for each"-loop in bc. For accessing each element of an array (the only collection-like type) one uses a straightforward for-loop.

a[0] = .123
a[1] = 234
a[3] = 95.6
for (i = 0; i < 4; i++) {
a[i]
}

[edit] Bracmat

Bracmat has a more or less traditional 'while' loop (whl'expression) which was introduced rather late in the history of Bracmat. Before that, tail recursion was a way to repeat something. But let us make a list first:

  ( list
= Afrikaans
Ελληνικά
עברית
മലയാളം
ئۇيغۇرچە
)

The 'while' solution. Use an auxiliary variable L that gets its head chopped off until nothing is left:

  !list:?L
& whl'(!L:%?language ?L&out$!language)

The tail-recursive solution. When the auxiliary variable is reduced to nothing, the loop fails. By adding the ~ flag to the initial invocation, failure is turned into success. This solution benefits from tail recursion optimization.

  !list:?L
& ( loop
=  !L:%?language ?L
& out$!language
& !loop
)
& ~!loop

A completly different way of iteration is by using a pattern that matches an element in the list, does something useful as a side effect and then fails, forcing bracmat to backtrack and try the next element in the list. The @ flag matches at most one element. The % flag matches at least one element. Together they ensure that exactly one language name is assigned to the variable language. After all elements have been done, control is passed to the rhs of the | operator.

  (   !list
 : ? (%@?language&out$!language&~) ?
|
)

[edit] C

C does not really have a native 'container' type, nor does it have a 'for each' type statement. The following shows how to loop through an array and print each element.

#include <stdio.h>
...
 
const char *list[] = {"Red","Green","Blue","Black","White"};
#define LIST_SIZE (sizeof(list)/sizeof(list[0]))
 
int ix;
for(ix=0; ix<LIST_SIZE; ix++) {
printf("%s\n", list[ix]);
}

The C language does, however, have a number of standard data structures that can be thought of as collections, and foreach can easily be made with a macro.

C string as a collection of char

 
#include <stdio.h>
#include <stdlib.h>
/* foreach macro for using a string as a collection of char */
#define foreach( ptrvar , strvar ) char* ptrvar; for( ptrvar=strvar ; (*ptrvar) != '\0' ; *ptrvar++)
 
int main(int argc,char* argv[]){
char* s1="abcdefg";
char* s2="123456789";
foreach( p1 , s1 ) {
printf("loop 1 %c\n",*p1);
}
foreach( p2 , s2 ){
printf("loop 2 %c\n",*p2);
}
exit(0);
return(0);
}
 

C int array as a collection of int (array size known at compile-time)

 
#include <stdio.h>
#include <stdlib.h>
int main(int argc,char* argv[]){
/* foreach macro viewing an array of int values as a collection of int values */
#define foreach( intpvar , intary ) int* intpvar; for( intpvar=intary; intpvar < (intary+(sizeof(intary)/sizeof(intary[0]))) ; intpvar++)
int a1[]={ 1 , 1 , 2 , 3 , 5 , 8 };
int a2[]={ 3 , 1 , 4 , 1, 5, 9 };
foreach( p1 , a1 ) {
printf("loop 1 %d\n",*p1);
}
foreach( p2 , a2 ){
printf("loop 2 %d\n",*p2);
}
exit(0);
return(0);
}
 

Most general: string or array as collection (collection size known at run-time)

Note: idxtype can be removed and typeof(col[0)] used in it's place with GCC
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc,char* argv[]){
#define foreach( idxtype , idxpvar , col , colsiz ) idxtype* idxpvar; for( idxpvar=col ; idxpvar < (col+(colsiz)) ; idxpvar++)
#define arraylen( ary ) ( sizeof(ary)/sizeof(ary[0]) )
char* c1="collection";
int c2[]={ 3 , 1 , 4 , 1, 5, 9 };
double* c3;
int c3len=4;
c3=(double*)calloc(c3len,sizeof(double));
c3[0]=1.2;c3[1]=3.4;c3[2]=5.6;c3[3]=7.8;
foreach( char,p1 , c1, strlen(c1) ) {
printf("loop 1 : %c\n",*p1);
}
foreach( int,p2 , c2, arraylen(c2) ){
printf("loop 2 : %d\n",*p2);
}
foreach( double,p3 , c3, c3len ){
printf("loop 3 : %3.1lf\n",*p3);
}
exit(0);
return(0);
}
 

[edit] C++

C++03 did not have a "for each" loop. The following is a generic loop which works with any standard container except for built-in arrays. The code snippet below assumes that the container type in question is typedef'd to container_type and the actual container object is named container.

for (container_type::iterator i = container.begin(); i != container.end(); ++i)
{
std::cout << *i << "\n";
}

However the idiomatic way to output a container would be

std::copy(container.begin(), container.end(),
std::ostream_iterator<container_type::value_type>(std::cout, "\n"));

There's also an algorithm named for_each. However, you need a function or function object to use it, e.g.

void print_element(container_type::value_type const& v)
{
std::cout << v << "\n";
}
 
...
std::for_each(container.begin(), container.end(), print_element);
Works with: C++11
for (auto element: container)
{
std::cout << element << "\n";
}

Here container is the container variable, element is the loop variable (initialized with each container element in turn), and auto means that the compiler should determine the correct type of that variable automatically. If the type is expensive to copy, a const reference can be used instead:

for (auto const& element: container)
{
std::cout << element << "\n";
}

Of course the container elements can also be changed by using a non-const reference (provided the container isn't itself constant):

for (auto&& element: container) //use a 'universal reference'
{
element += 42;
}

[edit] C#

string[] things = {"Apple", "Banana", "Coconut"};
 
foreach (string thing in things)
{
Console.WriteLine(thing);
}

[edit] Chapel

var food = ["Milk", "Bread", "Butter"];
for f in food do writeln(f);

[edit] Clojure

(doseq [item collection] (println item))

[edit] CMake

set(list one.c two.c three.c)
 
foreach(file ${list})
message(${file})
endforeach(file)

[edit] COBOL

The following is in the Managed COBOL dialect:

Translation of: C#
Works with: Visual COBOL
01  things occurs 3.
...
set content of things to ("Apple", "Banana", "Coconut")
perform varying thing as string through things
display thing
end-perform

[edit] ColdFusion

 
<Cfloop list="Fee, Fi, Foe, Fum" index="i">
<Cfoutput>#i#!</Cfoutput>
</Cfloop>
 

[edit] Common Lisp

(loop for i in list do (print i))

or

(map nil #'print list)

[edit] Creative Basic

 
DEF AnArray[11]:INT
 
AnArray=0,1,2,3,4,5,6,7,8,9,10
 
'A console only program will work without OPENCONSOLE and
'CLOSECONSOLE; however, it does not hurt to use them.
OPENCONSOLE
 
FOR X=0 TO 10
 
PRINT AnArray[X]
 
NEXT X
 
'keep the console from closing right away.
DO:UNTIL INKEY$<>""
 
CLOSECONSOLE
 
'because this is a console only program.
END
 

[edit] D

This works if collection is a string/array/associative array, or if implements an appropriate opApply function, or if it has the basic Range methods.

import std.stdio: writeln;
 
void main() {
auto collection1 = "ABC";
foreach (element; collection1)
writeln(element);
 
auto collection2 = [1, 2, 3];
foreach (element; collection1)
writeln(element);
 
auto collection3 = [1:10, 2:20, 3:30];
foreach (element; collection3)
writeln(element);
 
foreach (key, value; collection3)
writeln(key, " ", value);
}
Output:
A
B
C
A
B
C
10
20
30
1 10
2 20
3 30

[edit] Dao

items = { 1, 2, 3 }
for( item in items ) io.writeln( item )

[edit] Delphi

for..in loops were added in Delphi 2005.

Supports arrays (single, multidimensional, and dynamic), sets, strings, collections and any class or interface that implements GetEnumerator().

program LoopForEach;
 
{$APPTYPE CONSOLE}
 
var
s: string;
begin
for s in 'Hello' do
Writeln(s);
end.

Output:

H
e
l
l
o

[edit] E

for e in theCollection {
println(e)
}

In E, the for ... in ... loop is also used for iterating over numeric ranges; see Loop/For#E.

[edit] Efene

Any data structure can be printed as a whole, preformated:

io.format("~p~n", [Collection])

However, to iterate over each element of a list, Efene uses lists.map/2, except in the case of IO where lists.foreach/2 has to be used as the evaluation order is defined to be the same as the order of the elements in the list.

lists.foreach(fn (X) { io.format("~p~n", [X]) }, Collection)

[edit] Eiffel

Works with: EiffelStudio version 6.6 beta (with provisional loop syntax)

The iteration (foreach) form of the Eiffel loop construct is introduced by the keyword across.

            across my_list as ic loop print (ic.item) end

The local entity ic is an instance of the library class ITERATION_CURSOR. The cursor's feature item provides access to each structure element. Descendants of class ITERATION_CURSOR can be created to handle specialized iteration algorithms. The types of objects that can be iterated across (my_list in the example) are based on classes that inherit from the library class ITERABLE

[edit] Boolean expression variant

The iteration form of the Eiffel loop can also be used as a boolean expression when the keyword loop is replaced by either all (effecting universal quantification) or some (effecting existential quantification).

This iteration is a boolean expression which is true if all items in my_list have counts greater than three:

            across my_list as ic all ic.item.count > 3 end

Whereas, the following is true if at least one item has a count greater than three:

            across my_list as ic some ic.item.count > 3 end

[edit] Ela

[edit] Standard Approach

open console imperative
 
each writen [1..10]

Function 'each' is defined in imperative module as:

each f (x::xs) = f x $ each f xs
each _ [] = ()

This also can be accomplished using 'map':

open console list
 
_ = map writen [1..10]

[edit] Alternate Approach

each (x::xs) = writen x $ each xs
each [] = ()
 
each [1..10]

[edit] Emacs Lisp

For a list either dolist macro

(dolist (x '(1 2 3 4))
(message "x=%d" x))

or mapc function

(mapc (lambda (x)
(message "x=%d" x))
'(1 2 3 4))

dolist and mapc are both builtin in current Emacs. For past Emacs both can be had from cl.el with for instance (eval-when-compile (require 'cl)).

cl.el also offers a loop macro similar in style to Common Lisp.


[edit] Erlang

Any data structure can be printed as a whole, preformated:

io:format("~p~n",[Collection]).

However, to iterate over each element of a list, Erlang uses lists:map/2, except in the case of IO where lists:foreach/2 has to be used as the evaluation order is defined to be the same as the order of the elements in the list.

lists:foreach(fun(X) -> io:format("~p~n",[X]) end, Collection).

[edit] Euphoria

Works with: OpenEuphoria
 
include std/console.e
 
sequence s = {-2,-1,0,1,2} --print elements of a numerical list
for i = 1 to length(s) do
? s[i]
end for
 
puts(1,'\n')
 
s = {"Name","Date","Field1","Field2"} -- print elements of a list of 'strings'
for i = 1 to length(s) do
printf(1,"%s\n",{s[i]})
end for
 
puts(1,'\n')
 
for i = 1 to length(s) do -- print subelements of elements of a list of 'strings'
for j = 1 to length(s[i]) do
printf(1,"%s\n",s[i][j])
end for
puts(1,'\n')
end for
 
if getc(0) then end if
 
Output:
-2
-1
0
1
2

Name
Date
Field1
Field2

N
a
m
e

D
a
t
e

F
i
e
l
d
1

F
i
e
l
d
2

[edit] Factor

{ 1 2 4 } [ . ] each

[edit] Fantom

Use each method to iterate over a collection of items in a List.

class Main
{
public static Void main ()
{
Int[] collection := [1, 2, 3, 4, 5]
collection.each |Int item|
{
echo (item)
}
}
}

[edit] friendly interactive shell

Unlike, bash or csh, the PATH variable is automatically converted to real array.

for path in $PATH
echo You have $path in PATH.
end

Sample output:

You have /bin in PATH.
You have /usr/bin in PATH.

[edit] Fortran

program main
 
implicit none
 
integer :: i
character(len=5),dimension(5),parameter :: colors = ['Red ','Green','Blue ','Black','White']
 
!using a do loop:
do i=1,size(colors)
write(*,'(A)') colors(i)
end do
 
!this will also print each element:
write(*,'(A)') colors
 
end program main

[edit] Forth

create a 3 , 2 , 1 ,
: .array ( a len -- )
cells bounds do i @ . cell +loop ; \ 3 2 1

[edit] Frink

Frink's for loop is actually a "for each" loop which can iterate over built-in collection types including arrays, sets, dictionaries, enumerating expressions, and Java types such as Map, Iterator, Enumeration, etc.

 
array = [1, 2, 3, 5, 7]
for n = array
println[n]
 

[edit] F#

We can use for directly or list iteration.

for i in [1 .. 10] do printfn "%d" i
 
List.iter (fun i -> printfn "%d" i) [1 .. 10]

[edit] GAP

for p in AlternatingGroup(4) do
Print(p, "\n");
od;
 
()
(1,3,2)
(1,2,3)
(1,4,3)
(2,4,3)
(1,3)(2,4)
(1,2,4)
(1,4)(2,3)
(2,3,4)
(1,3,4)
(1,2)(3,4)
(1,4,2)

[edit] Go

range works with all of the built-in container-types. With one variable (i), it gives you the key/index of every item. With two variables (i, x), it gives you both the key/index and value/item. For channels, only the single-variable variant is allowed.

func printAll(values []int) {
for i, x := range values {
fmt.Printf("Item %d = %d\n", i, x)
}
}

[edit] Groovy

"for" loop:

def beatles = ["John", "Paul", "George", "Ringo"]
 
for(name in beatles) {
println name
}

"each()" method:
Though technically not a loop, most Groovy programmers would use the somewhat more terse "each()" method on the list itself in preference to the "for" loop construct.

beatles.each {
println it
}

Output (same for either):

John
Paul
George
Ringo

[edit] Haskell

import Control.Monad (forM_)
forM_ collect print

which is the same as

mapM_ print collect

[edit] Haxe

for(i in 1...10) Sys.println(i);

[edit] HicEst

CHARACTER days="Monday Tuesday Wednesday Thursday Friday Saturday Sunday "
 
items = INDEX(days, ' ', 256) ! 256 = count option
DO j = 1, items
EDIT(Text=days, ITeM=j, Parse=today)
WRITE() today
ENDDO

[edit] Io

collection foreach(println)

[edit] Icon and Unicon

The example below X can be a list, string, table or other data type.

procedure main()
X := [1,2,3,-5,6,9]
every x := !L do
write(x)
end

This loop can be written somewhat more concisely as:

every write(!L)

[edit] IWBASIC

 
== Linked List ==
 
DEF AList:POINTER
 
AList=ListCreate()
 
'Add items to the list.
DEF X:INT
 
FOR X=0 TO 10
POINTER Temp=ListAdd(AList,NEW(INT,1))
#<INT>temp=X
'The hash ("#") dereferencing operator is unique to IWBASIC and Creative Basic, and
'it is suitable for most basic pointer needs. IWBASIC also supports a "C style"
'dereferencing operator: "*". And that will work here too.
NEXT X
 
'A program compiled as console only does not need the commands to open and
'close the console. However, it does not hurt to use them.
OPENCONSOLE
 
'***Iterate the list with the "for each" loop***
FOR Temp=EACH AList AS INT
 
PRINT #Temp
 
NEXT
 
PRINT
 
'A press any key to continue message is automatic in a program compiled as a console only
program. I presume the compiler inserts the code.
CLOSECONSOLE
 
'Because this is a console only program.
END
 
== An Array ==
 
DEF AnArray[11]:INT
 
AnArray=0,1,2,3,4,5,6,7,8,9,10
 
OPENCONSOLE
 
FOR X=0 TO 10
 
PRINT AnArray[X]
 
NEXT X
 
PRINT
 
'a press any key message is automatic when compiled as console only.
CLOSECONSOLE
 
'Because this is a console only program.
END
 

[edit] J

smoutput each i.10

[edit] Java

Works with: Java version 1.5+
Iterable<Type> collect;
...
for(Type i:collect){
System.out.println(i);
}

This works for any array type as well as any type that implements the Iterable interface (including all Collections).

[edit] JavaScript

This works for any object, as well as arrays. It iterates over the keys of an object.

for (var a in o) {
print(o[a]);
}

However, it has the often unwanted feature that it lists inherited properties and methods of objects as well as the ones directly set on the object -- consider whether to filter out such properties inside the loop, for example:

for (var a in o) {
if (o.hasOwnProperty(a)) {
print(o[a]);
}
}
Works with: JavaScript version 1.6
Deprecated

There is also a for each in construct that iterates over the values of an object:

h = {"one":1, "two":2, "three":3}
for (x in h) print(x);
/*
two
one
three
*/

 
for each (y in h) print(y);
/*
2
1
3
*/
Works with: ECMAScript version 6th edition

There is also a for of construct that iterates over the values of an object:

h = {"one":1, "two":2, "three":3}
for (x in h) print(x);
/*
two
one
three
*/

 
for (y of h) print(y);
/*
2
1
3
*/

[edit] Julia

Translation of: Python
for i in collection
println(i)
end

The Julia for statement is always a "foreach", and the built-in start:end or start:step:end "range" syntax can be used for iteration over arithmetic sequences. Many Julia objects support iteration: arrays and tuples iterate over each item, strings iterate over each character, dictionaries iterate over (key,value) pairs, numeric scalars provide a length-1 iteration over their value, and so on.

[edit] jq

Iterables:

In this section, the array defined by "example" is used as an example:

def example: [1,2];

jq has two types of iterables -- JSON arrays and JSON objects. In both cases, the ".[]" filter may be used to iterate through the values, it being understand that for objects, the "values" are the values associated with the keys:

example | .[]
# or equivalently: example[]
{"a":1, "b":2} | .[]
# or equivalently: {"a":1, "b":2}[]

In both cases, the output is the stream consisting of the values 1 followed by 2.

Sometimes it is necessary to use an alternative to ".[]". For example, one might want to generate an index along with the array elements. In such cases, the "range(m;n)" generator, which performs a similar role to C's "for(i=m; i<n; i++)", can be used for array. Here is how range/2 would be used to perform the task for an array:

example | . as $a | range(0; length) | $a[.]

For JSON objects, the corresponding technique involves using keys, e.g.

 
{"a":1, "b":2} | . as $o | keys | map( [., $o[.]] )
 

produces:

[["a",1],["b",2]]


Strings:

To convert the constituent characters (or technically, codepoints) of a string into a stream of values, there are two techniques illustrated by these examples:

"abc" | . as $s | range(0;length) | $s[.:.+1]
 
"abc" | explode | map( [.]|implode) | .[]

In both cases, the result is the stream of values: "a", "b", "c".

[edit] Lasso

array(1,2,3) => foreach { stdoutnl(#1) }
with i in array(1,2,3) do { stdoutnl(#i) }

[edit] K

   {`0:$x} ' !10
   _sin ' (1; 2; 3;)

[edit] LFE

(: lists foreach
(lambda (x)
(: io format '"item: ~p~n" (list x)))
(: lists seq 1 10))
 

[edit] LabVIEW

LabVIEW has a feature known as an Auto-Indexed Tunnel. It is the very small orange box on the lower left of the for loop.
This image is a VI Snippet, an executable image of LabVIEW code. The LabVIEW version is shown on the top-right hand corner. You can download it, then drag-and-drop it onto the LabVIEW block diagram from a file browser, and it will appear as runnable, editable code.
LabVIEW Loops Foreach.png

[edit] Lang5

: >>say.(*) . ;
5 iota >>say.

[edit] Liberty BASIC

The most natural way is to use a csv list with a sentinel value.

in$      ="Not,Hardly,Just,Adequately,Quite,Really,Very,Fantastically,xyzzy"
element$ =""
i =1 ' used to point to successive elements
 
do
element$ =word$( in$, i, ",")
if element$ ="xyzzy" then exit do
print element$; " good!"
i =i +1
loop until 1 =2
 
end
Not good!
Hardly good!
Just good!
Adequately good!
Quite good!
Really good!
Very good!
Fantastically good!

[edit] Lisaac

"Lisaac loop foreach".split.foreach { word : STRING;
word.print;
'\n'.print;
};

[edit]

foreach [red green blue] [print ?]

[edit] Lua

Lua has 2 built-in iterators over tables.

pairs() iterates over all entries in a table, but in no particular order:

t={monday=1, tuesday=2, wednesday=3, thursday=4, friday=5, saturday=6, sunday=0, [7]="fooday"}
for key, value in pairs(t) do
print(value, key)
end

Output:

0	sunday
fooday	7
2	tuesday
3	wednesday
5	friday
4	thursday
6	saturday
1	monday

ipairs() iterates over table entries with positive integer keys, and is used to iterate over lists in order.

l={'monday', 'tuesday', 'wednesday', 'thursday', 'friday', 'saturday', 'sunday', not_a_number='fooday', [0]='today', [-1]='yesterday' }
for key, value in ipairs(l) do
print(key, value)
end

Output:

1	monday
2	tuesday
3	wednesday
4	thursday
5	friday
6	saturday
7	sunday

Note that ipairs() ignores non-numeric and non-positive integer keys.

[edit] Maple

 
for p in [2, 3, 5, 7] do
print(p);
end do;
 

[edit] Mathematica

Foreach over list of strings

s = (StringSplit@Import["ExampleData/USConstitution.txt"])[[1;;7]]; 
Do[
Print@i,
{i, s}
]

Output:

We
the
People
of
the
United
States,

[edit] MATLAB / Octave

    list1 = [1,5,6,7,-7,-9];   
for k = list1, % list1 must be a row vector (i.e. array of size 1xn)
printf('%i\n',k)
end;
    list2 = {'AA','BB','CC'};
for k = list2, % list2 must be a row vector (i.e. array of size 1xn)
printf('%s\n',k{1})
end;

A vectorized version of the code is

  printf('%d\n',list1);  
printf('%s\n',list2{:});

[edit] Maxima

for n in [2, 3, 5, 7] do print(n);

[edit] MAXScript

 
arr = for i in 1 to 50 collect ("Number: " + (random 10 99) as string)
makeuniquearray arr
sort arr
 
for i in arr do print i as string
 

[edit] Metafont

If we have a list of arbitrary items, we can simply use for:

for x = "mary", "had", "a", "little", "lamb": message x; endfor
end

The list can be generated in place by any suitable macro or another loop... e.g. let us suppose we have things like a[n] defined (with maximum n being 10). Then

for x = for i = 1 upto 9: a[i], endfor, a[10]: show x; endfor
end

works more like a foreach; we could make a macro to hide the strangeness of such a code.

[edit] MOO

things = {"Apple", "Banana", "Coconut"};
 
for thing in (things)
player:tell(thing);
endfor

[edit] Nemerle

This works on anything which implements the IEnumerable interface.

def things = ["Apple", "Banana", "Coconut"];
 
foreach (thing in things) WriteLine(thing.ToLower());
foreach (i in [5, 10 .. 100]) Write($"$i\t");

[edit] NetRexx

/* NetRexx */
options replace format comments java crossref savelog symbols nobinary
 
say
say 'Loops/Foreach'
 
days = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday']
daysl = Arrays.asList(days)
daysi = daysl.iterator
 
loop while daysi.hasNext
say daysi.next
end

[edit] NewLISP

(map println '(Apple Banana Coconut))

[edit] Nimrod

var list: seq[string] = @[]
list.add("lorem")
list.add("ipsum")
list.add("dolor")
for i in items(list):
echo(i)

Output:

lorem
ipsum
dolor

[edit] Objective-C

Works with: Objective-C version 2.0+
Works with: GNUstep
Works with: Cocoa
NSArray *collect;
//...
for(Type i in collect){
NSLog(@"%@", i);
}

collect can be any object that adopts the NSFastEnumeration protocol.

Or (always using OpenStep compatible frameworks):

Works with: Objective-C version <2.0
NSArray *collect;
//...
NSEnumerator *enm = [collect objectEnumerator];
id i;
while( (i = [enm nextObject]) ) {
// do something with object i
}

[edit] Objeck

fruits := ["Apple", "Banana", "Coconut"];
each(i : fruits) {
fruits[i]->PrintLine();
};

[edit] OCaml

List of integers:

List.iter
(fun i -> Printf.printf "%d\n" i)
collect_list

Array of integers:

Array.iter
(fun i -> Printf.printf "%d\n" i)
collect_array

[edit] Octave

a = [ 1,4,3,2 ];
b = [ 1,2,3,4; 5,6,7,8 ];
for v = a
disp(v); % output single values: 1,4,3,2
endfor
for v = b
disp(v); % v is the column vector [1;5], then [2;6] ...
endfor

We can also iterate over structures:

x.a = [ 10, 11, 12 ];
x.b = { "Cell", "ul", "ar" };
for [ val, key ] = x
disp(key);
disp(val);
endfor

[edit] ooRexx

The OVER loop control keyword is used to select each item in a collection in turn. Open Object Rexx allows the DO block structure keyword to be used to start a loop for backward compatibility with classic Rexx; the LOOP keyword is preferred here as it is self-documenting.

/* Rexx */
say
say 'Loops/Foreach'
out = ''
 
days = .array~of('Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday')
 
loop daysi over days
out ||= daysi' '
end daysi
say out~strip()
 
exit
 

Output:

Loops/Foreach
Sunday Monday Tuesday Wednesday Thursday Friday Saturday

[edit] Oz

declare
MyList = [1 2 3 4]
in
{ForAll MyList Show}
 
%% or:
for E in MyList do {Show E} end

[edit] PARI/GP

for(i=1,#v,print(v[i]))

or (PARI/GP >= 2.4)

apply(x->print(x),v)

[edit] Pascal

See Delphi

[edit] Perl

foreach my $i (@collection) {
print "$i\n";
}

The keyword for can be used instead of foreach. If a loop variable (here $i) is not given, then $_ is used.

A more compact notation using perl statement modifier:

print "$_\n"  foreach @collection

In perl, it is possible to loop against an explicit list, so there is no need to define a container:

foreach $l ( "apples", "bananas", "cherries" ) {
print "I like $l\n";
}

[edit] Perl 6

Works with: Rakudo version #21 "Seattle"
say $_ for @collection;

Perl 6 leaves off the each from foreach, leaving us with for instead. The variable $_ refers to the current element, unless you assign a name to it using ->.

for @collection -> $currentElement { say $currentElement; }

[edit] PHP

foreach ($collect as $i) {
echo "$i\n";
}
 
foreach ($collect as $key => $i) {
echo "\$collect[$key] = $i\n";
}

foreach can also iterate over objects. By default it iterates over all visible fields of an object.

[edit] PicoLisp

(mapc println '(Apple Banana Coconut))

[edit] Pike

int main(){
array(int|string) collect = ({109, "Hi", "asdf", "qwerty"});
foreach(collect, int|string elem){
write(elem + "\n");
}
}

Iterating over the keys and values of a mapping (dictionary):

int main(){
mapping(string:string) coll = (["foo":"asdf", "bar":"qwer", "quux":"zxcv"]);
foreach (coll;string key;string val)
write(key+" --> "+val+"\n");
}
}

[edit] PL/I

declare A(10) fixed binary;
do i = lbound(A,1) to hbound(A,1);
put skip list (A(i));
end;

[edit] Pop11

Iteration over list:

lvars el, lst = [1 2 3 4 foo bar];
for el in lst do
printf(el,'%p\n');
endfor;

[edit] PostScript

The forall operator performs a loop over a collection (array, string or dictionary). Strings and arrays can be treated very much the same:

[1 5 3 2] { = } forall
(abc) { = } forall

but dictionaries take a little more work since a key/value pair is pushed on the stack in each iteration:

<</a 25 /b 42>> {
exch (Key: ) print
=
(Value: ) print
=
} forall

[edit] PowerShell

foreach ($x in $collection) {
Write-Host $x
}

[edit] Prolog

For example :

?- foreach(member(X, [red,green,blue,black,white]), writeln(X)).
red
green
blue
black
white
true.
 

[edit] PureBasic

Works for LinkedLists and Maps

ForEach element()
PrintN(element())
Next

[edit] Python

for i in collection:
print i

Note: The Python for statement is always a "foreach" ... and the range() and xrange() built-in functions are used to generate lists of indexes over which it will iterate as necessary. The majority of Python objects support iteration. Lists and tuples iterate over each item, strings iterate over each character, dictionaries iterate over keys, files iterate over lines, and so on.

For example:

lines = words = characters = 0
f = open('somefile','r')
for eachline in f:
lines += 1
for eachword in eachline.split():
words += 1
for eachchar in eachword:
characters += 1
 
print lines, words, characters

Whether for loops over the elements of the collection in order depends on the collection having an inherent order or not. Elements of strings (i.e. characters), tuples and lists, for example, are ordered but the order of elements in dictionaries and sets is not defined.

One can loop over the key/value pairs of a dictionary in alphabetic or numeric key order by sorting the sequence of keys, provided that the keys are all of comparable types. In Python 3.x a sequence of mixed numeric and string elements is not sortable (at least not with the default invocation of sorted()), whereas in Python 2.x numeric types are sorted according to their string representation by default:

d = {3: "Earth", 1: "Mercury", 4: "Mars", 2: "Venus"}
for k in sorted(d):
print("%i: %s" % (k, d[k]))
 
d = {"London": "United Kingdom", "Berlin": "Germany", "Rome": "Italy", "Paris": "France"}
for k in sorted(d):
print("%s: %s" % (k, d[k]))
Works with: Python version 2.x
d = {"fortytwo": 42, 3.14159: "pi", 23: "twentythree", "zero": 0, 13: "thirteen"}
for k in sorted(d):
print("%s: %s" % (k, d[k]))

[edit] R

a <- list("First", "Second", "Third", 5, 6)
for(i in a) print(i)

[edit] Racket

 
#lang racket
 
;; an example sequence
(define sequence '("something" 1 2 "foo"))
 
;; works for any sequence
(for ([i sequence])
(displayln i))
 

[edit] REBOL

rebol [
Title: "Loop/Foreach"
Author: oofoe
Date: 2009-12-19
URL: http://rosettacode.org/wiki/Loop/Foreach
]

 
x: [Sork Gun Blues Neds Thirst Fright Catur]
 
foreach i x [prin rejoin [i "day "]] print ""
 
; REBOL also has the 'forall' construct, which provides the rest of
; the list from the current position.
 
forall x [prin rejoin [x/1 "day "]] print ""

Output:

Sorkday Gunday Bluesday Nedsday Thirstday Frightday Caturday
Sorkday Gunday Bluesday Nedsday Thirstday Frightday Caturday

[edit] Retro

Retro has an each@ combinator for operating on elements of various data structures. A hook (<each@>) exists to allow for user-defined data structures to be added.

( Strings: this will display the ASCII code for each character in a string )
"This is a message" [ @ putn space ] ^types'STRING each@
 
( Array: display each element )
needs array'
[ 1 2 3 ] ^array'fromQuote [ @ putn space ] ^types'ARRAY each@
 
( Linked List: using the dictionary as an example, display each name )
last [ d->name puts space ] ^types'LIST each@
 
( Generic Buffers; display each value in a buffer )
create foo
1 , 3 , 5 ,
 
foo 3 [ @ putn space ] ^types'BUFFER each@

[edit] REXX

days = 'zuntik montik dinstik mitvokh donershtik fraytik shabes'
 
do j=1 for words(days) /*loop through days of the week. */
say word(days,j) /*display the weekday to screen. */
end /*j*/
/*stick a fork in it, we're done.*/

[edit] Ruby

for i in collection do
puts i
end

This is syntactic sugar for:

collection.each do |i|
puts i
end

There are various flavours of each that may be class-dependent: String#each_char, Array#each_index, Hash#each_key, etc


[edit] Run BASIC

t$={Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday"
 
while word$(t$,i+1,",") <> ""
i = i + 1
print word$(t$,i,",")
wend

[edit] Salmon

iterate (x; ["Red", "Green", "Blue"])
x!;

output:

Red
Green
Blue

[edit] SAS

/* Initialize an array with integers 1 to 10, and print their sum */
data _null_;
array a a1-a10;
n=1;
do over a;
a=n;
n=n+1;
end;
s=sum(of a{*});
put s;
run;

[edit] Sather

class MAIN is
main is
num:ARRAY{INT} := |1, 5, 4, 3, 10|;
loop
-- the iterator elt! behaves like a "foreach",
-- yielding the next element of the array at each iteration
#OUT + num.elt! + "\n";
end;
end;
end;

[edit] Scala

val collection = Array(1, 2, 3, 4)
for (element <- collection)
println(element)

Alternatively:

for (element <- 1 to 4)
println(element)

[edit] Scheme

List:

(for-each
(lambda (i) (display i) (newline))
the_list)

[edit] Seed7

The for loop of Seed7 can be used to loop over the elements of a container.

$ include "seed7_05.s7i";
 
var array string: things is [] ("Apple", "Banana", "Coconut");
 
const proc: main is func
local
var string: thing is "";
begin
for thing range things do
writeln(thing);
end for;
end func;

[edit] Sidef

foreach [1,2,3] { |i|
say i;
}

same as:

[1,2,3].each { |i|
say i;
}

[edit] Slate

c do: [| :obj | print: obj].

[edit] Smalltalk

aCollection do: [ :element | element displayNl ].

(Provided that the objects in the collection understand the displayNl method).

[edit] Sparkling

Sparkling currently has no "foreach" construct, but there's a "foreach" function in the standard library:

let hash = { "foo": 42, "bar": 1337, "baz": "qux" };
foreach(hash, function(key, val) {
print(key, " -> ", val);
});

[edit] Standard ML

List of integers:

app
(fn i => print (Int.toString i ^ "\n"))
collect_list

Array of integers:

Array.app
(fn i => print (Int.toString i ^ "\n"))
collect_array

[edit] Suneido

for i in #(1, 2, 3)
Print(i)

[edit] Swift

for i in [1,2,3] {
println(i)
}

This works for any type that conforms to the Sequence protocol (including arrays, collections, generators, ranges, and strings).

[edit] SystemVerilog

program main;
int values[$];
 
initial begin
values = '{ 1, 3, 7, 11 };
foreach (values[i]) begin
$display( "%0d --> %0d", i, values[i] );
end
end
endprogram

[edit] Tcl

foreach i {foo bar baz} {
puts "$i"
}

Note that foreach also accepts multiple variables:

foreach {x y} {1 2 3 4} {
puts "$x,$y"
}

And also multiple lists:

foreach i {1 2 3} j {a b c} {
puts "$i,$j"
}

Or any combination of variables/list:

foreach i {1 2 3} {x y} {a b c d e f} {
puts "$i,$x,$y"
}

[edit] TI-89 BASIC

Local i,strs
Define strs = {"Lorem","ipsum","dolor"}
For i, 1, dim(strs)
Disp strs[i]
EndFor

[edit] Trith

[1 2 3 4 5] [print] each

[edit] TUSCRIPT

$$ MODE TUSCRIPT
week="Monday'Tuesday'Wednesday'Thursday'Friday'Saterday'Sunday"
LOOP day=week
PRINT day
ENDLOOP

Output:

Monday
Tuesday
Wednesday
Thursday
Friday
Saterday
Sunday

[edit] UNIX Shell

To iterate any single list, you use a for loop.

Works with: Bourne Shell
for file in *.sh; do
echo "filename is $file"
done

If the list is in a shell parameter (like PATH), you adjust IFS.

Works with: Bourne Shell
PATH=/usr/bin:/bin:/usr/sbin:/sbin:/usr/X11R6/bin:/usr/local/bin
 
oldifs=$IFS
IFS=:
for dir in $PATH; do
echo search $dir
done
IFS=$oldifs

Some shells have real arrays. The for loop can also iterate these.

Works with: Bash
collection=("first" "second" "third" "fourth" "something else")
for x in "${collection[@]}"; do
echo "$x"
done
Works with: pdksh version 5.2.14
set -A collection "first" "second" "third" "fourth" "something else"
for x in "${collection[@]}"; do
echo "$x"
done

[edit] C Shell

set collection=(first second third fourth "something else")
foreach x ($collection:q)
echo $x:q
end

[edit] V

[1 2 3] [puts] step

[edit] VBScript

dim items(2)
items(0)="Apple"
items(1)="Orange"
items(2)="Banana"
 
For Each x in items
WScript.Echo x
Next

[edit] Vim Script

Vim Script's for-loop is actually a foreach-loop and iterates through a list.

for i in ["alpha", "beta", 42, 5.54]
echo i
endfor

[edit] Visual Basic .NET

Dim list As New List(Of String)
list.Add("Car")
list.Add("Boat")
list.Add("Train")
 
For Each item In list
Console.WriteLine(item)
Next

[edit] Wart

each x '(1 2 3)
prn x

[edit] XPL0

Translation of C example:

include c:\cxpl\codes;
int List, I;
[List:= ["Red", "Green", "Blue", "Black", "White"];
for I:= 0, 5-1 do
[Text(0, List(I)); CrLf(0)];
]

[edit] XSLT

For-each is the only iteration construct that is built into XSLT. All other iteration is either implied by applying a template to all members matching an XPath expression, or built from recursive application of a template. You have access to something like a loop counter with the one-based "position()" function.

<fo:block font-weight="bold">Adults:</fo:block>
<xsl:for-each select="person[@age &gt;= 21]">
<fo:block><xsl:value-of select="position()"/>. <xsl:value-of select="@name"/></fo:block>
</xsl:for-each>

[edit] zkl

Translation of: XPL0
foreach c in (T("Red","Green","Blue","Black","White"))
{ print(c," "); }
Output:
Red Green Blue Black White

Other forms of foreach, one that breaks apart a container into elements and one line nested loops.

foreach x,y,z in (T(T(1,2,3), T(4,5,6))) { println(x,y,z) }
foreach x,y,z in (T(1,2,3), T(4,5), T(6)){ println(x,y,z) }
Output:
123
456
146
156
246
256
346
356
Personal tools
Namespaces

Variants
Actions
Community
Explore
Misc
Toolbox