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Loops/Foreach
From Rosetta Code
[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;
[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] 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 done:
for(i=1; i <= length(strs); i++) {
print strs[i]
}
[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]);
}
[edit] C++
C++ does not (yet) 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::output_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);
The next version of the standard will allow the following simplified syntax:
#include <iterator_concepts>
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:
#include <iterator_concepts>
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).
[edit] C#
string[] things = {"Apple", "Banana", "Coconut"};
foreach (string thing in things)
{
Console.WriteLine(thing);
}
[edit] Clojure
(doseq [item collection] (println item))
[edit] Common Lisp
(loop for i in list do (print i))
or
(map nil #'print list)
[edit] D
This works if collection is an array/associative array type or any type that implements an appropriate opApply function.
foreach(element ; collection)
writefln(element);
[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] 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] Factor
{ 1 2 4 } [ . ] each
[edit] Forth
create a 3 , 2 , 1 ,
: .array ( a len -- )
cells bounds do i @ . cell +loop ; \ 3 2 1
[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] Haskell
import Control.Monad (forM_)
forM_ collect print
which is the same as
mapM_ print collect
[edit] HaXe
for(i in 1...10) Lib.println(i);
[edit] Io
collection foreach(println)
[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.
Works with: JavaScript version 1.6
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
*/
[edit] Lisaac
"Lisaac loop foreach".split.foreach { word : STRING;
word.print;
'\n'.print;
};
[edit] Logo
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] MAXScript
for i in collect do
(
print i
)
[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] 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] 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] Oz
declare
MyList = [1 2 3 4]
in
{ForAll MyList Show}
%% or:
for E in MyList do {Show E} end
[edit] Perl
foreach my $i (@collect) {
print "$i\n";
}
The keyword for can be used instead of foreach. If a loop variable (here $i) is not given, then $_ is used.
[edit] Perl 6
Works with: Rakudo version #21 "Seattle"
for @collect -> $i {
say $i;
}
foreach no longer exists. But as in Perl 5, you can omit the loop variable (and here, the ->) to use $_ implicitly.
[edit] PHP
foreach ($collect as $i) {
echo "$i\n";
}
foreach ($collect as $key => $i) {
echo "\$collect[$key] = $i\n";
}
foreach can also iterate over objects. By default it iterates over all visible fields of an object.
[edit] PicoLisp
(mapc println '(Apple Banana Coconut))
[edit] Pike
int main(){
array(string) collect = ({109, "Hi", "asdf", "qwerty"});
foreach(collect, string elem){
write(elem + "\n");
}
}
[edit] PL/I
declare A(10) fixed binary;
do i = lbound(A,1) to hbound(A,1);
put skip list (A(i));
end;
[edit] Pop11
Iteration over list:
lvars el, lst = [1 2 3 4 foo bar];
for el in lst do
printf(el,'%p\n');
endfor;
[edit] PowerShell
foreach ($x in $collection) {
Write-Host $x
}
[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:
chracters += 1
print lines, words, characters
[edit] R
a <- list("First", "Second", "Third", 5, 6)
for(i in a) print(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] REXX
Standard REXX:
days = "sunday monday tuesday wednesday thursday friday saturday"
do d = 1 to words(days)
say word(days,d)
end
or:
days = "sunday monday tuesday wednesday thursday friday saturday"
hlp = days
do while hlp <> ""
parse var hlp item hlp
say item
end
Works with: oorexx:
colors = .bag~of("red","green","blue","pink")
do c over colors
say c
end
[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] Scheme
List:
(for-each
(lambda (i) (display i) (newline))
the_list)
[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] 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] 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] UNIX Shell
for file in *.sh; do
echo "filename is $file"
done
[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] 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] 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 >= 21]">
<fo:block><xsl:value-of select="position()"/>. <xsl:value-of select="@name"/></fo:block>
</xsl:for-each>
