Loops/Foreach: Difference between revisions
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Most general: string or array as collection (collection size known at run-time) |
Most general: string or array as collection (collection size known at run-time) |
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: ''Note: idxtype can be removed and [http://gcc.gnu.org/onlinedocs/gcc/Typeof.html typeof |
: ''Note: idxtype can be removed and [http://gcc.gnu.org/onlinedocs/gcc/Typeof.html typeof(col[0])] used in it's place with [[GCC]]'' |
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<lang c> |
<lang c> |
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#include <stdio.h> |
#include <stdio.h> |
Revision as of 16:05, 16 July 2012
![Task](http://static.miraheze.org/rosettacodewiki/thumb/b/ba/Rcode-button-task-crushed.png/64px-Rcode-button-task-crushed.png)
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.
ACL2
<lang Lisp>(defun print-list (xs)
(if (endp xs) nil (prog2$ (cw "~x0~%" (first xs)) (print-list (rest xs)))))</lang>
> (print-list (list 1 "a" 1/2 (list 1 2) 'sym)) 1 "a" 1/2 (1 2) SYM NIL
Ada
arrays
<lang Ada>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;</lang>
doubly linked lists
<lang Ada>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;</lang>
vectors
<lang Ada>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;</lang>
Aikido
Aikido's foreach
loop allows iteration through multiple value types.
strings
<lang aikido>var str = "hello world" foreach ch str { // you can also use an optional 'in'
println (ch) // one character at a time
}</lang>
vectors
<lang aikido>var vec = [1,2,3,4] foreach v vec { // you can also use an optional 'in'
println (v)
}</lang>
maps
<lang aikido>var cities = {"San Ramon": 50000, "Walnut Creek": 70000, "San Francisco": 700000} // map literal foreach city cities {
println (city.first + " has population " + city.second)
}</lang>
integers
<lang aikido>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)
}</lang>
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
<lang aikido>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)
}</lang>
Coroutines
Aikido supports coroutines. The foreach operator may be used to iterate thorough the generated values. <lang aikido>// 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)
}</lang>
Files
If you open a file you can iterate through all the lines <lang aikido>var s = openin ("input.txt") foreach line s {
print (line)
}</lang>
Enumerations
<lang aikido>enum Color {
RED, GREEN, BLUE
}
foreach color Color {
println (color)
}</lang>
ALGOL 68
<lang algol68>[]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</lang> 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.
AmigaE
<lang 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</lang>
AutoHotkey
<lang AutoHotkey>string = mary,had,a,little,lamb Loop, Parse, string, `,
MsgBox %A_LoopField%</lang>
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).
<lang awk>BEGIN {
split("Mary had a little lamb", strs, " ") for(el in strs) { print strs[el] }
}</lang> 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 done: <lang awk>for(i=1; i <= length(strs); i++) {
print strs[i]
}</lang>
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:
<lang bracmat> ( list
= Afrikaans Ελληνικά עברית മലയാളം ئۇيغۇرچە )</lang>
The 'while' solution. Use an auxiliary variable L
that gets its head chopped off until nothing is left:
<lang bracmat> !list:?L
& whl'(!L:%?language ?L&out$!language)</lang>
The tail-recursive solution. When the auxiliary variable is reduced to nothing, the loop fails. By adding the ~
flag to the initial invocation, failure is turned into success. This solution benefits from tail recursion optimization.
<lang bracmat> !list:?L
& ( loop
= !L:%?language ?L & out$!language & !loop )
& ~!loop</lang>
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.
<lang bracmat> ( !list
: ? (%@?language&out$!language&~) ? | )</lang>
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. <lang c>#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]);
}</lang>
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 <lang c>
- 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); } </lang>
C int array as a collection of int (array size known at compile-time) <lang c>
- 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); } </lang>
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
<lang c>
- 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); } </lang>
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. <lang cpp>for (container_type::iterator i = container.begin(); i != container.end(); ++i) {
std::cout << *i << "\n";
}</lang> However the idiomatic way to output a container would be <lang cpp>std::copy(container.begin(), container.end(),
std::output_iterator<container_type::value_type>(std::cout, "\n"));</lang>
There's also an algorithm named for_each. However, you need a function or function object to use it, e.g. <lang cpp>void print_element(container_type::value_type const& v) {
std::cout << v << "\n";
}
...
std::for_each(container.begin(), container.end(), print_element);</lang>
<lang cpp>#include <iterator_concepts>
for (auto element: container) {
std::cout << element << "\n";
}</lang> 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: <lang cpp>#include <iterator_concepts>
for (auto const& element: container) {
std::cout << element << "\n";
}</lang> Of course the container elements can also be changed by using a non-const reference (provided the container isn't itself constant).
C#
<lang csharp>string[] things = {"Apple", "Banana", "Coconut"};
foreach (string thing in things) {
Console.WriteLine(thing);
}</lang>
Clojure
<lang lisp>(doseq [item collection] (println item))</lang>
CMake
<lang cmake>set(list one.c two.c three.c)
foreach(file ${list})
message(${file})
endforeach(file)</lang>
Common Lisp
<lang lisp>(loop for i in list do (print i))</lang> or <lang lisp>(map nil #'print list)</lang>
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. <lang d>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);
}</lang>
- Output:
A B C A B C 10 20 30 1 10 2 20 3 30
Dao
<lang dao>items = { 1, 2, 3 } for( item in items ) io.writeln( item )</lang>
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(). <lang Delphi>program LoopForEach;
{$APPTYPE CONSOLE}
var
s: string;
begin
for s in 'Hello' do Writeln(s);
end.</lang> Output:
H e l l o
E
<lang e>for e in theCollection {
println(e)
}</lang> In E, the for ... in ... loop is also used for iterating over numeric ranges; see Loop/For#E.
Efene
Any data structure can be printed as a whole, preformated: <lang efene>io.format("~p~n", [Collection])</lang> 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. <lang efene>lists.foreach(fn (X) { io.format("~p~n", [X]) }, Collection)</lang>
Eiffel
The iteration (foreach) form of the Eiffel loop construct is introduced by the keyword across
.
<lang eiffel > across my_list as ic loop print (ic.item) end</lang>
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
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:
<lang eiffel> across my_list as ic all ic.item.count > 3 end</lang>
Whereas, the following is true if at least one item has a count greater than three:
<lang eiffel> across my_list as ic some ic.item.count > 3 end</lang>
Ela
Standard Approach
<lang ela>open console imperative
each writen [1..10]</lang> Function 'each' is defined in imperative module as: <lang ela>each f (x::xs) = f x $ each f xs
each _ [] = ()</lang>
This also can be accomplished using 'map': <lang ela>open console list
map writen [1..10]</lang>
Alternate Approach
<lang ela>each (x::xs) = writen x $ each xs each [] = ()
each [1..10]</lang>
Erlang
Any data structure can be printed as a whole, preformated: <lang erlang>io:format("~p~n",[Collection]).</lang> 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. <lang erlang>lists:foreach(fun(X) -> io:format("~p~n",[X]) end, Collection).</lang>
Factor
<lang factor>{ 1 2 4 } [ . ] each</lang>
Fantom
Use each
method to iterate over a collection of items in a List
.
<lang fantom>class Main
{
public static Void main () { Int[] collection := [1, 2, 3, 4, 5] collection.each |Int item| { echo (item) } }
}</lang>
Fortran
<lang 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</lang>
Forth
<lang forth>create a 3 , 2 , 1 ,
- .array ( a len -- )
cells bounds do i @ . cell +loop ; \ 3 2 1</lang>
F#
We can use for directly or list iteration. <lang fsharp>for i in [1 .. 10] do printfn "%d" i
List.iter (fun i -> printfn "%d" i) [1 .. 10]</lang>
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.
<lang go>func printAll(values []int) {
for i, x := range values { fmt.Printf("Item %d = %d\n", i, x) }
}</lang>
Groovy
"for" loop: <lang groovy>def beatles = ["John", "Paul", "George", "Ringo"]
for(name in beatles) {
println name
}</lang>
"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.
<lang groovy>beatles.each {
println it
}</lang> Output (same for either):
John Paul George Ringo
Haskell
<lang haskell>import Control.Monad (forM_) forM_ collect print</lang> which is the same as <lang haskell>mapM_ print collect</lang>
HaXe
<lang HaXe>for(i in 1...10) Lib.println(i);</lang>
HicEst
<lang 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</lang>
Io
<lang io>collection foreach(println)</lang>
Icon and Unicon
The example below X can be a list, string, table or other data type. <lang Icon>procedure main() X := [1,2,3,-5,6,9] every x := !L do
write(x)
end</lang> This loop can be written somewhat more concisely as: <lang Icon>every write(!L)</lang>
J
<lang J>smoutput each i.10</lang>
Java
<lang java>Iterable<Type> collect; ... for(Type i:collect){
System.out.println(i);
}</lang> This works for any array type as well as any type that implements the Iterable interface (including all Collections).
JavaScript
This works for any object, as well as arrays. It iterates over the keys of an object. <lang JavaScript>for (var a in o) {
print(o[a]);
}</lang> 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: <lang JavaScript>for (var a in o) {
if (o.hasOwnProperty(a)) { print(o[a]); }
}</lang>
There is also a for each in construct that iterates over the values of an object: <lang JavaScript>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
- /</lang>
K
<lang K> {`0:$x} ' !10</lang> <lang K> _sin ' (1; 2; 3;)</lang>
LabVIEW
LabVIEW has a feature known as an Auto-Indexed Tunnel. It is the very small orange box on the lower left of the for loop.
This image is a VI Snippet, an executable image of LabVIEW code. The LabVIEW version is shown on the top-right hand corner. You can download it, then drag-and-drop it onto the LabVIEW block diagram from a file browser, and it will appear as runnable, editable code.
Liberty BASIC
The most natural way is to use a csv list with a sentinel value. <lang lb>in$ ="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</lang>
Not good! Hardly good! Just good! Adequately good! Quite good! Really good! Very good! Fantastically good!
Lisaac
<lang Lisaac>"Lisaac loop foreach".split.foreach { word : STRING;
word.print; '\n'.print;
};</lang>
Logo
<lang logo>foreach [red green blue] [print ?]</lang>
Lua
Lua has 2 built-in iterators over tables.
pairs()
iterates over all entries in a table, but in no particular order:
<lang lua>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</lang> 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.
<lang lua>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</lang> 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.
Mathematica
Foreach over list of strings <lang mathematica>s = (StringSplit@Import["ExampleData/USConstitution.txt"])1;;7; Do[
Print@i, {i, s}
]</lang> Output:
We the People of the United States,
MATLAB / Octave
<lang Matlab> 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; </lang>
<lang Matlab> 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; </lang>
A vectorized version of the code is <lang Matlab> printf('%d\n',list1);
printf('%s\n',list2{:}); </lang>
Maxima
<lang maxima>for n in [2, 3, 5, 7] do print(n);</lang>
MAXScript
<lang maxscript>for i in collect do (
print i
)</lang>
Metafont
If we have a list of arbitrary items, we can simply use for: <lang metafont>for x = "mary", "had", "a", "little", "lamb": message x; endfor end</lang> 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 <lang metafont>for x = for i = 1 upto 9: a[i], endfor, a[10]: show x; endfor end</lang> works more like a foreach; we could make a macro to hide the strangeness of such a code.
MOO
<lang moo>things = {"Apple", "Banana", "Coconut"};
for thing in (things)
player:tell(thing);
endfor</lang>
Nemerle
This works on anything which implements the IEnumerable interface. <lang Nemerle>def things = ["Apple", "Banana", "Coconut"];
foreach (thing in things) WriteLine(thing.ToLower()); foreach (i in [5, 10 .. 100]) Write($"$i\t");</lang>
NetRexx
<lang 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</lang>
Nimrod
<lang nimrod>var list: seq[string] = @[] list.add("lorem") list.add("ipsum") list.add("dolor") for i in items(list):
echo(i)</lang>
Output:
lorem ipsum dolor
Objective-C
<lang objc>NSArray *collect; //... for(Type i in collect){
NSLog(@"%@", i);
}</lang> collect can be any object that adopts the NSFastEnumeration protocol.
Or (always using OpenStep compatible frameworks):
<lang objc>NSArray *collect; //... NSEnumerator *enm = [collect objectEnumerator]; id i; while( (i = [enm nextObject]) ) {
// do something with object i
}</lang>
Objeck
<lang objeck>fruits := ["Apple", "Banana", "Coconut"]; each(i : fruits) {
fruits[i]->PrintLine();
};</lang>
OCaml
List of integers: <lang ocaml>List.iter
(fun i -> Printf.printf "%d\n" i) collect_list</lang>
Array of integers: <lang ocaml>Array.iter
(fun i -> Printf.printf "%d\n" i) collect_array</lang>
Octave
<lang 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</lang> We can also iterate over structures: <lang octave>x.a = [ 10, 11, 12 ]; x.b = { "Cell", "ul", "ar" }; for [ val, key ] = x
disp(key); disp(val);
endfor</lang>
Oz
<lang oz>declare
MyList = [1 2 3 4]
in
{ForAll MyList Show}
%% or: for E in MyList do {Show E} end</lang>
PARI/GP
<lang parigp>for(i=1,#v,print(v[i]))</lang>
or (PARI/GP >= 2.4)
<lang parigp>apply(x->print(x),v)</lang>
Pascal
See Delphi
Perl
<lang perl>foreach my $i (@collection) {
print "$i\n";
}</lang>
The keyword for
can be used instead of foreach
. If a loop variable (here $i
) is not given, then $_
is used.
A more compact notation using perl statement modifier: <lang perl>print "$_\n" foreach @collection</lang>
Perl 6
<lang perl6>say $_ for @collection;</lang> 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 ->. <lang perl6>for @collection -> $currentElement { say $currentElement; }</lang>
PHP
<lang php>foreach ($collect as $i) {
echo "$i\n";
}
foreach ($collect as $key => $i) {
echo "\$collect[$key] = $i\n";
}</lang>
foreach
can also iterate over objects. By default it iterates over all visible fields of an object.
PicoLisp
<lang PicoLisp>(mapc println '(Apple Banana Coconut))</lang>
Pike
<lang pike>int main(){
array(int|string) collect = ({109, "Hi", "asdf", "qwerty"}); foreach(collect, int|string elem){ write(elem + "\n"); }
}</lang> Iterating over the keys and values of a mapping (dictionary): <lang pike>int main(){
mapping(string:string) coll = (["foo":"asdf", "bar":"qwer", "quux":"zxcv"]); foreach (coll;string key;string val) write(key+" --> "+val+"\n"); }
}</lang>
PL/I
<lang PL/I>declare A(10) fixed binary; do i = lbound(A,1) to hbound(A,1);
put skip list (A(i));
end;</lang>
Pop11
Iteration over list: <lang pop11>lvars el, lst = [1 2 3 4 foo bar]; for el in lst do
printf(el,'%p\n');
endfor;</lang>
PostScript
The forall
operator performs a loop over a collection (array, string or dictionary). Strings and arrays can be treated very much the same:
<lang postscript>[1 5 3 2] { = } forall
(abc) { = } forall</lang>
but dictionaries take a little more work since a key/value pair is pushed on the stack in each iteration:
<lang postscript><</a 25 /b 42>> {
exch (Key: ) print = (Value: ) print =
} forall</lang>
PowerShell
<lang powershell>foreach ($x in $collection) {
Write-Host $x
}</lang>
PureBasic
Works for LinkedLists and Maps <lang PureBasic>ForEach element()
PrintN(element())
Next</lang>
Python
<lang python>for i in collection:
print i</lang>
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: <lang python>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: chracters += 1
print lines, words, characters</lang>
R
<lang R>a <- list("First", "Second", "Third", 5, 6) for(i in a) print(i)</lang>
REBOL
<lang 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 ""</lang> Output:
Sorkday Gunday Bluesday Nedsday Thirstday Frightday Caturday Sorkday Gunday Bluesday Nedsday Thirstday Frightday Caturday
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. <lang Retro>( 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@</lang>
REXX
Standard REXX: <lang rexx>days = "sunday monday tuesday wednesday thursday friday saturday"
do d = 1 to words(days)
say word(days,d)
end</lang> or: <lang rexx>days = "sunday monday tuesday wednesday thursday friday saturday"
hlp = days do while hlp <> ""
parse var hlp item hlp say item
end</lang>
:
<lang rexx>colors = .bag~of("red","green","blue","pink")
do c over colors
say c
end</lang>
Ruby
<lang ruby>for i in collection do
puts i
end</lang> This is syntactic sugar for: <lang ruby>collection.each do |i|
puts i
end</lang>
There are various flavours of each
that may be class-dependent: String#each_char, Array#each_index, Hash#each_key, etc
Run BASIC
<lang runbasic>t$={Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday"
while word$(t$,i+1,",") <> ""
i = i + 1 print word$(t$,i,",")
wend</lang>
Salmon
<lang Salmon>iterate (x; ["Red", "Green", "Blue"])
x!;</lang>
output:
Red Green Blue
SAS
<lang 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;</lang>
Sather
<lang 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;</lang>
Scala
<lang scala>val collection = Array(1, 2, 3, 4) for (element <- collection)
println(element)</lang>
Alternatively: <lang scala>for (element <- 1 to 4)
println(element)</lang>
Scheme
List: <lang scheme>(for-each
(lambda (i) (display i) (newline)) the_list)</lang>
Seed7
The for loop of Seed7 can be used to loop over the elements of a container. <lang seed7>$ 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;</lang>
Slate
<lang slate>c do: [| :obj | print: obj].</lang>
Smalltalk
<lang smalltalk>aCollection do: [ :element | element displayNl ].</lang>
(Provided that the objects in the collection understand the displayNl
method).
Standard ML
List of integers: <lang sml>app
(fn i => print (Int.toString i ^ "\n")) collect_list</lang>
Array of integers: <lang sml>Array.app
(fn i => print (Int.toString i ^ "\n")) collect_array</lang>
Suneido
<lang Suneido>for i in #(1, 2, 3)
Print(i)</lang>
SystemVerilog
<lang SystemVerilog>program main;
int values[$];
initial begin values = '{ 1, 3, 7, 11 }; foreach (values[i]) begin $display( "%0d --> %0d", i, values[i] ); end end
endprogram</lang>
Tcl
<lang tcl>foreach i {foo bar baz} {
puts "$i"
}</lang> Note that foreach also accepts multiple variables: <lang tcl>foreach {x y} {1 2 3 4} {
puts "$x,$y"
}</lang> And also multiple lists: <lang tcl>foreach i {1 2 3} j {a b c} {
puts "$i,$j"
}</lang> Or any combination of variables/list: <lang tcl>foreach i {1 2 3} {x y} {a b c d e f} {
puts "$i,$x,$y"
}</lang>
TI-89 BASIC
<lang ti89b>Local i,strs Define strs = {"Lorem","ipsum","dolor"} For i, 1, dim(strs)
Disp strs[i]
EndFor</lang>
Trith
<lang trith>[1 2 3 4 5] [print] each</lang>
TUSCRIPT
<lang tuscript>$$ MODE TUSCRIPT week="Monday'Tuesday'Wednesday'Thursday'Friday'Saterday'Sunday" LOOP day=week PRINT day ENDLOOP</lang> Output:
Monday Tuesday Wednesday Thursday Friday Saterday Sunday
UNIX Shell
To iterate any single list, you use a for
loop.
<lang bash>for file in *.sh; do
echo "filename is $file"
done</lang>
If the list is in a shell parameter (like PATH
), you adjust IFS
.
<lang bash>PATH=/usr/bin:/bin:/usr/sbin:/sbin:/usr/X11R6/bin:/usr/local/bin
oldifs=$IFS IFS=: for dir in $PATH; do
echo search $dir
done
IFS=$oldifs</lang>
Some shells have real arrays. The for
loop can also iterate these.
<lang bash>collection=("first" "second" "third" "fourth" "something else") for x in "${collection[@]}"; do
echo "$x"
done</lang>
<lang bash>set -A collection "first" "second" "third" "fourth" "something else" for x in "${collection[@]}"; do
echo "$x"
done</lang>
C Shell
<lang csh>set collection=(first second third fourth "something else") foreach x ($collection:q) echo $x:q end</lang>
V
<lang v>[1 2 3] [puts] step</lang>
VBScript
<lang vbscript>dim items(2) items(0)="Apple" items(1)="Orange" items(2)="Banana"
For Each x in items
WScript.Echo x
Next</lang>
Visual Basic .NET
<lang vbnet>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</lang>
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. <lang xml><fo:block font-weight="bold">Adults:</fo:block> <xsl:for-each select="person[@age >= 21]">
<fo:block><xsl:value-of select="position()"/>. <xsl:value-of select="@name"/></fo:block>
</xsl:for-each></lang>
- Programming Tasks
- Iteration
- ACL2
- Ada
- Aikido
- ALGOL 68
- AmigaE
- AutoHotkey
- AWK
- Bracmat
- C
- C++
- C sharp
- Clojure
- CMake
- Common Lisp
- D
- Dao
- Delphi
- E
- Efene
- Eiffel
- Ela
- Erlang
- Factor
- Fantom
- Fortran
- Forth
- F Sharp
- Go
- Groovy
- Haskell
- HaXe
- HicEst
- Io
- Icon
- Unicon
- J
- Java
- JavaScript
- K
- LabVIEW
- Liberty BASIC
- Lisaac
- Logo
- Lua
- Mathematica
- MATLAB
- Octave
- Maxima
- MAXScript
- Metafont
- MOO
- Nemerle
- NetRexx
- Nimrod
- Objective-C
- Objeck
- OCaml
- Oz
- PARI/GP
- Pascal
- Perl
- Perl 6
- PHP
- PicoLisp
- Pike
- PL/I
- Pop11
- PostScript
- PowerShell
- PureBasic
- Python
- R
- REBOL
- Retro
- REXX
- Ruby
- Run BASIC
- Salmon
- SAS
- Sather
- Scala
- Scheme
- Seed7
- Slate
- Smalltalk
- Standard ML
- Suneido
- SystemVerilog
- Tcl
- TI-89 BASIC
- Trith
- TUSCRIPT
- UNIX Shell
- C Shell
- V
- VBScript
- Visual Basic .NET
- XSLT
- GUISS/Omit