Flatten a list
From Rosetta Code
You are encouraged to solve this task according to the task description, using any language you may know.
Write a function to flatten the nesting in an arbitrary list of values. Your program should work on the equivalent of this list:
[[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]
Where the correct result would be the list:
[1, 2, 3, 4, 5, 6, 7, 8]
C.f. Tree traversal
[edit] ACL2
(defun flatten (tr)
(cond ((null tr) nil)
((atom tr) (list tr))
(t (append (flatten (first tr))
(flatten (rest tr))))))
[edit] ActionScript
function flatten(input:Array):Array {
var output:Array = new Array();
for (var i:uint = 0; i < input.length; i++) {
//typeof returns "object" when applied to arrays. This line recursively evaluates nested arrays,
// although it may break if the array contains objects that are not arrays.
if (typeof input[i]=="object") {
output=output.concat(flatten(input[i]));
} else {
output.push(input[i]);
}
}
return output;
}
[edit] Aikido
function flatten (list, result) {
foreach item list {
if (typeof(item) == "vector") {
flatten (item, result)
} else {
result.append (item)
}
}
}
var l = [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]
var newl = []
flatten (l, newl)
// print out the nicely formatted result list
print ('[')
var comma = ""
foreach item newl {
print (comma + item)
comma = ", "
}
println("]")
Output:
[1, 2, 3, 4, 5, 6, 7, 8]
[edit] Aime
void
show_list(list l)
{
integer i;
text s;
o_text("[");
s = "";
i = 0;
while (i < l_length(l)) {
o_text(s);
if (l_s_integer(l, i)) {
o_integer(l_q_integer(l, i));
} else {
show_list(l_q_list(l, i));
}
s = ", ";
i += 1;
}
o_text("]");
}
void
flat(list c, list l)
{
integer i;
i = 0;
while (i < l_length(l)) {
if (l_s_integer(l, i)) {
lb_p_integer(c, l_q_integer(l, i));
} else {
flat(c, l_q_list(l, i));
}
i += 1;
}
}
list
flatten(list l)
{
list c;
flat(c, l);
return c;
}
list
nl(...)
{
integer i;
list l;
i = 0;
while (i < count()) {
l_append(l, $i);
i += 1;
}
return l;
}
integer
main(void)
{
list l;
l_set(l, nl(nl(1), 2, nl(nl(3, 4), 5), nl(nl(nl())), nl(nl(nl(6))), 7, 8,
nl()));
show_list(l);
o_byte('\n');
show_list(flatten(l));
o_byte('\n');
return 0;
}
Output:
[[1], 2, [[3, 4], 5], [[[]]], [[[6]]], 7, 8, []] [1, 2, 3, 4, 5, 6, 7, 8]
[edit] ALGOL 68
Flattening is built in to all of Algol68's transput routines. The following example also uses widening, where scalars are converted into arrays.
main:(
[][][]INT list = ((1), 2, ((3,4), 5), ((())), (((6))), 7, 8, ());
print((list, new line))
)
Output:
+1 +2 +3 +4 +5 +6 +7 +8
[edit] AppleScript
my_flatten({{1}, 2, {{3, 4}, 5}, {{{}}}, {{{6}}}, 7, 8, {}})
on my_flatten(aList)
if class of aList is not list then
return {aList}
else if length of aList is 0 then
return aList
else
return my_flatten(first item of aList) & (my_flatten(rest of aList))
end if
end my_flatten
[edit] AutoHotkey
AutoHotkey doesn't have built in list data type. This examples simulates a list in a tree type object and flattens that tree.
list := object(1, object(1, 1), 2, 2, 3, object(1, object(1, 3, 2, 4)
, 2, 5), 4, object(1, object(1, object(1, object()))), 5
, object(1, object(1, 6)), 6, 7, 7, 8, 9, object())
msgbox % objPrint(list) ; (( 1 ) 2 (( 3 4 ) 5 )(((())))(( 6 )) 7 8 ())
msgbox % objPrint(objFlatten(list)) ; ( 1 2 3 4 5 6 7 8 )
return
!r::reload
!q::exitapp
objPrint(ast, reserved=0)
{
if !isobject(ast)
return " " ast " "
if !reserved
reserved := object("seen" . &ast, 1) ; to keep track of unique objects within top object
enum := ast._newenum()
while enum[key, value]
{
if reserved["seen" . &value]
continue ; don't copy repeat objects (circular references)
; string .= key . ": " . objPrint(value, reserved)
string .= objPrint(value, reserved)
}
return "(" string ")"
}
objFlatten(ast)
{
if !isobject(ast)
return ast
flat := object() ; flat object
enum := ast._newenum()
while enum[key, value]
{
if !isobject(value)
flat._Insert(value)
else
{
next := objFlatten(value)
loop % next._MaxIndex()
flat._Insert(next[A_Index])
}
}
return flat
}
[edit] Bracmat
A list is automatically flattened during evaluation if the items are separated by either commas, plusses, asterisks or white spaces.
On top of that, lists separated with white space, plusses or asterisks have 'nil'-elements removed when evaluated. (nil-elements are empty strings, 0 and 1 respectively.)
On top of that, lists separated with plusses or asterisks have their elements sorted and, if possible, combined when evaluated.
A list that should not be flattened upon evaluation can be separated with dots.
( (myList = ((1), 2, ((3,4), 5), ((())), (((6))), 7, 8, ()))
& put$("Unevaluated:")
& lst$myList
& !myList:?myList { the expression !list evaluates myList }
& put$("Flattened:")
& lst$myList
)
[edit] Brat
array.prototype.flatten = {
true? my.empty?
{ [] }
{ true? my.first.array?
{ my.first.flatten + my.rest.flatten }
{ [my.first] + my.rest.flatten }
}
}
list = [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]
p "List: #{list}"
p "Flattened: #{list.flatten}"
[edit] Burlesque
Usually flattening Blocks is done with the Concat command but it only removes one level of nesting therefore it is required to chain Concat calls until the Block does not contain Blocks anymore.
blsq ) {{1} 2 {{3 4} 5} {{{}}} {{{6}}} 7 8 {}}{\[}{)to{"Block"==}ay}w!
{1 2 3 4 5 6 7 8}
[edit] C
#include <stdio.h>output
#include <stdlib.h>
#include <string.h>
typedef struct list_t list_t, *list;
struct list_t{
int is_list, ival; /* ival is either the integer value or list length */
list *lst;
};
list new_list()
{
list x = malloc(sizeof(list_t));
x->ival = 0;
x->is_list = 1;
x->lst = 0;
return x;
}
void append(list parent, list child)
{
parent->lst = realloc(parent->lst, sizeof(list) * (parent->ival + 1));
parent->lst[parent->ival++] = child;
}
list from_string(char *s, char **e, list parent)
{
list ret = 0;
if (!parent) parent = new_list();
while (*s != '\0') {
if (*s == ']') {
if (e) *e = s + 1;
return parent;
}
if (*s == '[') {
ret = new_list();
ret->is_list = 1;
ret->ival = 0;
append(parent, ret);
from_string(s + 1, &s, ret);
continue;
}
if (*s >= '0' && *s <= '9') {
ret = new_list();
ret->is_list = 0;
ret->ival = strtol(s, &s, 10);
append(parent, ret);
continue;
}
s++;
}
if (e) *e = s;
return parent;
}
void show_list(list l)
{
int i;
if (!l) return;
if (!l->is_list) {
printf("%d", l->ival);
return;
}
printf("[");
for (i = 0; i < l->ival; i++) {
show_list(l->lst[i]);
if (i < l->ival - 1) printf(", ");
}
printf("]");
}
list flatten(list from, list to)
{
int i;
list t;
if (!to) to = new_list();
if (!from->is_list) {
t = new_list();
*t = *from;
append(to, t);
} else
for (i = 0; i < from->ival; i++)
flatten(from->lst[i], to);
return to;
}
void delete_list(list l)
{
int i;
if (!l) return;
if (l->is_list && l->ival) {
for (i = 0; i < l->ival; i++)
delete_list(l->lst[i]);
free(l->lst);
}
free(l);
}
int main()
{
list l = from_string("[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []", 0, 0);
printf("Nested: ");
show_list(l);
printf("\n");
list flat = flatten(l, 0);
printf("Flattened: ");
show_list(flat);
/* delete_list(l); delete_list(flat); */
return 0;
}
Nested: [[1], 2, [[3, 4], 5], [[[]]], [[[6]]], 7, 8, []] Flattened: [1, 2, 3, 4, 5, 6, 7, 8]
[edit] C++
#include <list>
#include <boost/any.hpp>
typedef std::list<boost::any> anylist;
void flatten(std::list<boost::any>& list)
{
typedef anylist::iterator iterator;
iterator current = list.begin();
while (current != list.end())
{
if (current->type() == typeid(anylist))
{
iterator next = current;
++next;
list.splice(next, boost::any_cast<anylist&>(*current));
current = list.erase(current);
}
else
++current;
}
}
Use example:
Since C++ currently doesn't have nice syntax for initializing lists, this includes a simple parser to create lists of integers and sublists. Also, there's no standard way to output this type of list, so some output code is added as well.
#include <cctype>
#include <iostream>
// *******************
// * the list parser *
// *******************
void skipwhite(char const** s)
{
while (**s && std::isspace((unsigned char)**s))
{
++*s;
}
}
anylist create_anylist_i(char const** s)
{
anylist result;
skipwhite(s);
if (**s != '[')
throw "Not a list";
++*s;
while (true)
{
skipwhite(s);
if (!**s)
throw "Error";
else if (**s == ']')
{
++*s;
return result;
}
else if (**s == '[')
result.push_back(create_anylist_i(s));
else if (std::isdigit((unsigned char)**s))
{
int i = 0;
while (std::isdigit((unsigned char)**s))
{
i = 10*i + (**s - '0');
++*s;
}
result.push_back(i);
}
else
throw "Error";
skipwhite(s);
if (**s != ',' && **s != ']')
throw "Error";
if (**s == ',')
++*s;
}
}
anylist create_anylist(char const* i)
{
return create_anylist_i(&i);
}
// *************************
// * printing nested lists *
// *************************
void print_list(anylist const& list);
void print_item(boost::any const& a)
{
if (a.type() == typeid(int))
std::cout << boost::any_cast<int>(a);
else if (a.type() == typeid(anylist))
print_list(boost::any_cast<anylist const&>(a));
else
std::cout << "???";
}
void print_list(anylist const& list)
{
std::cout << '[';
anylist::const_iterator iter = list.begin();
while (iter != list.end())
{
print_item(*iter);
++iter;
if (iter != list.end())
std::cout << ", ";
}
std::cout << ']';
}
// ***************************
// * The actual test program *
// ***************************
int main()
{
anylist list =
create_anylist("[[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]");
print_list(list);
std::cout << "\n";
flatten(list);
print_list(list);
std::cout << "\n";
}
The output of this program is
[[1], 2, [[3, 4], 5], [[[]]], [[[6]]], 7, 8, []] [1, 2, 3, 4, 5, 6, 7, 8]
[edit] C#
Actual Workhorse code
using System;
using System.Collections;
using System.Linq;
namespace RosettaCodeTasks
{
static class FlattenList
{
public static ArrayList Flatten(this ArrayList List)
{
ArrayList NewList = new ArrayList ( );
NewList.AddRange ( List );
while ( NewList.OfType<ArrayList> ( ).Count ( ) > 0 )
{
int index = NewList.IndexOf ( NewList.OfType<ArrayList> ( ).ElementAt ( 0 ) );
ArrayList Temp = (ArrayList)NewList[index];
NewList.RemoveAt ( index );
NewList.InsertRange ( index, Temp );
}
return NewList;
}
}
}
Method showing population of arraylist and usage of flatten method
using System;
using System.Collections;
namespace RosettaCodeTasks
{
class Program
{
static void Main ( string[ ] args )
{
ArrayList Parent = new ArrayList ( );
Parent.Add ( new ArrayList ( ) );
((ArrayList)Parent[0]).Add ( 1 );
Parent.Add ( 2 );
Parent.Add ( new ArrayList ( ) );
( (ArrayList)Parent[2] ).Add ( new ArrayList ( ) );
( (ArrayList)( (ArrayList)Parent[2] )[0] ).Add ( 3 );
( (ArrayList)( (ArrayList)Parent[2] )[0] ).Add ( 4 );
( (ArrayList)Parent[2] ).Add ( 5 );
Parent.Add ( new ArrayList ( ) );
( (ArrayList)Parent[3] ).Add ( new ArrayList ( ) );
( (ArrayList)( (ArrayList)Parent[3] )[0] ).Add ( new ArrayList ( ) );
Parent.Add ( new ArrayList ( ) );
( (ArrayList)Parent[4] ).Add ( new ArrayList ( ) );
( (ArrayList)( (ArrayList)Parent[4] )[0] ).Add ( new ArrayList ( ) );
( (ArrayList)( (ArrayList)( (ArrayList)( (ArrayList)Parent[4] )[0] )[0] ) ).Add ( 6 );
Parent.Add ( 7 );
Parent.Add ( 8 );
Parent.Add ( new ArrayList ( ) );
foreach ( Object o in Parent.Flatten ( ) )
{
Console.WriteLine ( o.ToString ( ) );
}
}
}
}
[edit] Clojure
The following returns a lazy sequence of the flattened data structure.
(defn flatten [coll]
(lazy-seq
(when-let [s (seq coll)]
(if (coll? (first s))
(concat (flatten (first s)) (flatten (rest s)))
(cons (first s) (flatten (rest s)))))))
The built-in flatten is implemented as:
(defn flatten [x]
(filter (complement sequential?)
(rest (tree-seq sequential? seq x))))
[edit] CoffeeScript
flatten = (arr) ->
arr.reduce ((xs, el) ->
if Array.isArray el
xs.concat flatten el
else
xs.concat [el]), []
# test
list = [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]
console.log flatten list
Ouput:
> coffee foo.coffee
[ 1, 2, 3, 4, 5, 6, 7, 8 ]
[edit] Common Lisp
(defun flatten (structure)
(cond ((null structure) nil)
((atom structure) `(,structure))
(t (mapcan #'flatten structure))))
Note that since the empty list is the same thing as nil, a tree of boolean false values cannot be flattened; they will disappear.
[edit] D
Instead of a Java-like class-based version, this version minimizes heap activity using a tagged union.
import std.stdio, std.algorithm, std.conv, std.range;
struct TreeList(T) {
union { // A tagged union
TreeList[] arr; // it's a node
T data; // it's a leaf
}
bool isArray = true; // = contains an arr on default.
static TreeList opCall(A...)(A items) /*const*/ pure nothrow {
TreeList result;
foreach (i, el; items)
static if (is(A[i] == T)) {
TreeList item;
item.isArray = false;
item.data = el;
result.arr ~= item;
} else
result.arr ~= el;
return result;
}
string toString() const {
return isArray ? text(arr) : text(data);
}
}
T[] flatten(T)(in TreeList!T t) /*pure nothrow*/ {
if (t.isArray)
return t.arr.map!flatten().join();
else
return [t.data];
}
void main() {
alias TreeList!int L;
static assert(L.sizeof == 12);
auto l = L(L(1), 2, L(L(3,4), 5), L(L(L())), L(L(L(6))),7,8,L());
writeln(l);
writeln(flatten(l));
}
- Output:
[[1], 2, [[3, 4], 5], [[[]]], [[[6]]], 7, 8, []] [1, 2, 3, 4, 5, 6, 7, 8]
[edit] With an Algebraic Data Type
A shorter and more cryptic version.
import std.stdio, std.variant, std.range, std.algorithm;
alias T = Algebraic!(int, This[]);
int[] flatten(T t) {
return t.peek!int ? [t.get!int] : t.get!(T[])().map!flatten.join;
}
void main() {
T([T([ T(1) ]),
T(2),
T([ T([ T(3), T(4) ]), T(5) ]),
T([ T([ T( T[].init ) ]) ]),
T([ T([ T([ T(6) ]) ]) ]),
T(7),
T(8),
T( T[].init )
]).flatten.writeln;
}
- Output:
[1, 2, 3, 4, 5, 6, 7, 8]
[edit] E
def flatten(nested) {
def flat := [].diverge()
def recur(x) {
switch (x) {
match list :List { for elem in list { recur(elem) } }
match other { flat.push(other) }
}
}
recur(nested)
return flat.snapshot()
}
? flatten([[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []])
# value: [1, 2, 3, 4, 5, 6, 7, 8]
[edit] Ela
This implementation can flattern any given list:
xs = [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]
flat = flat' []
where flat' n [] = n
flat' n (x::xs)
| x is List = flat' (flat' n xs) x
| else = x :: flat' n xs
flat xs
Output:
[1,2,3,4,5,6,7,8]
An alternative solution:
flat [] = []
flat (x::xs)
| x is List = flat x ++ flat xs
| else = x :: flat xs
[edit] Emacs Lisp
(defun flatten (mylist)
(cond
((null mylist) nil)
((atom mylist) (list mylist))
(t
(append (flatten (car mylist)) (flatten (cdr mylist))))))
[edit] Erlang
There's a standard function (lists:flatten/2) that does it more efficiently, but this is the cleanest implementation you could have;
flatten([]) -> [];
flatten([H|T]) -> flatten(H) ++ flatten(T);
flatten(H) -> [H].
[edit] Euphoria
sequence a = {{1}, 2, {{3, 4}, 5}, {{{}}}, {{{6}}}, 7, 8, {}}
function flatten( object s )
sequence res = {}
if sequence( s ) then
for i = 1 to length( s ) do
sequence c = flatten( s[ i ] )
if length( c ) > 0 then
res &= c
end if
end for
else
if length( s ) > 0 then
res = { s }
end if
end if
return res
end function
? a
? flatten(a)
Output
{
{1},
2,
{
{3,4},
5
},
{
{{}}
},
{
{
{6}
}
},
7,
8,
{}
}
{1,2,3,4,5,6,7,8}
[edit] F#
As with Haskell and OCaml we have to define our list as an algebraic data type, to be strongly typed:
type 'a ll =
| I of 'a // leaf Item
| L of 'a ll list // ' <- confine the syntax colouring confusion
let rec flatten = function
| [] -> []
| (I x)::y -> x :: (flatten y)
| (L x)::y -> List.append (flatten x) (flatten y)
printfn "%A" (flatten [L([I(1)]); I(2); L([L([I(3);I(4)]); I(5)]); L([L([L([])])]); L([L([L([I(6)])])]); I(7); I(8); L([])])
// -> [1; 2; 3; 4; 5; 6; 7; 8]
[edit] Factor
USE: sequences.deep
( scratchpad ) { { 1 } 2 { { 3 4 } 5 } { { { } } } { { { 6 } } } 7 8 { } } flatten .
{ 1 2 3 4 5 6 7 8 }
[edit] Fantom
class Main
{
// uses recursion to flatten a list
static List myflatten (List items)
{
List result := [,]
items.each |item|
{
if (item is List)
result.addAll (myflatten(item))
else
result.add (item)
}
return result
}
public static Void main ()
{
List sample := [[1], 2, [[3,4], 5], [[[,]]], [[[6]]], 7, 8, [,]]
// there is a built-in flatten method for lists
echo ("Flattened list 1: " + sample.flatten)
// or use the function 'myflatten'
echo ("Flattened list 2: " + myflatten (sample))
}
}
[edit] Frink
a = [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]
println[flatten[a]]
[edit] GAP
Flat([[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]);
[edit] Go
package main
import "fmt"
func list(s ...interface{}) []interface{} {
return s
}
func main() {
s := list(list(1),
2,
list(list(3, 4), 5),
list(list(list())),
list(list(list(6))),
7,
8,
list(),
)
fmt.Println(s)
fmt.Println(flatten(s))
}
func flatten(s []interface{}) (r []int) {
for _, e := range s {
switch i := e.(type) {
case int:
r = append(r, i)
case []interface{}:
r = append(r, flatten(i)...)
}
}
return
}
Output:
[[1] 2 [[3 4] 5] [[[]]] [[[6]]] 7 8 []] [1 2 3 4 5 6 7 8]
In the code above, flatten uses an easy-to-read type switch to extract ints and return an int slice. The version below is generalized to return a flattened slice of interface{} type, which can of course refer to objects of any type, and not just int. Also, just to show a variation in programming style, a type assertion is used rather than a type switch.
func flatten(s []interface{}) (r []interface{}) {
for _, e := range s {
if i, ok := e.([]interface{}); ok {
r = append(r, flatten(i)...)
} else {
r = append(r, e)
}
}
return
}
[edit] Groovy
List.flatten() is a Groovy built-in that returns a flattened copy of the source list:
assert [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []].flatten() == [1, 2, 3, 4, 5, 6, 7, 8]
[edit] Haskell
In Haskell we have to interpret this structure as an algebraic data type.
import Data.Tree
-- [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]
-- implemented as multiway tree:
-- Data.Tree represents trees where nodes have values too, unlike the trees in our problem.
-- so we use a list as that value, where a node will have an empty list value,
-- and a leaf will have a one-element list value and no subtrees
list :: Tree [Int]
list = Node [] [
Node [] [Node [1] []],
Node [2] [],
Node [] [
Node [] [ Node [3] [],Node [4] []],
Node [5] []
],
Node [] [Node [] [Node [] []]],
Node [] [Node [] [Node [6] []]],
Node [7] [],
Node [8] [],
Node [] []
]
flattenList = concat.flatten
Flattening the list:
*Main> flattenList list [1,2,3,4,5,6,7,8]
Alternately:
data Tree a = Leaf a | Node [Tree a]
flatten :: Tree a -> [a]
flatten (Leaf x) = [x]
flatten (Node xs) = concatMap flatten xs
main = print $ flatten $ Node [Node [Leaf 1],
Leaf 2,
Node [Node [Leaf 3, Leaf 4], Leaf 5],
Node [Node [Node []]],
Node [Node [Node [Leaf 6]]],
Leaf 7,
Leaf 8,
Node []]
-- output: [1,2,3,4,5,6,7,8]
Yet another choice, custom data structure, efficient lazy flattening:
(This is unnecessary; since Haskell is lazy, the previous solution will only do just as much work as necessary for each element that is requested from the resulting list.)
data NestedList a = NList [NestedList a] | Entry a
flatten :: NestedList a -> [a]
flatten nl = flatten' nl []
where
-- By passing through a list which the results will be preprended to we allow efficient lazy evaluation
flatten' :: NestedList a -> [a] -> [a]
flatten' (Entry a) cont = a:cont
flatten' (NList entries) cont = foldr flatten' cont entries
example :: NestedList Int
example = NList [ NList [Entry 1], Entry 2, NList [NList [Entry 3, Entry 4], Entry 5], NList [NList [NList []]], NList [ NList [ NList [Entry 6]]], Entry 7, Entry 8, NList []]
main :: IO ()
main = print $ flatten example
-- output [1,2,3,4,5,6,7,8]
[edit] Icon and Unicon
The following procedure solves the task using a string representation of nested lists and cares not if the list is well formed or not.
link strings # for compress,deletec,pretrim
procedure sflatten(s) # uninteresting string solution
return pretrim(trim(compress(deletec(s,'[ ]'),',') ,','),',')
end
The solution uses several procedures from strings in the IPL
This procedure is more in the spirit of the task handling actual lists rather than representations. It uses a recursive approach using some of the built-in list manipulation functions and operators.
procedure flatten(L) # in the spirt of the problem a structure
local l,x
l := []
every x := !L do
if type(x) == "list" then l |||:= flatten(x)
else put(l,x)
return l
end
Finally a demo routine to drive these and a helper to show how it works.
procedure main()
write(sflatten(" [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]"))
writelist(flatten( [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]))
end
procedure writelist(L)
writes("[")
every writes(" ",image(!L))
write(" ]")
return
end
[edit] Ioke
iik> [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []] flatten
[[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []] flatten
+> [1, 2, 3, 4, 5, 6, 7, 8]
[edit] J
Solution:
flatten =: [: ; <S:0
Example:
NB. create and display nested noun li
]li =. (<1) ; 2; ((<3; 4); 5) ; ((<a:)) ; ((<(<6))) ; 7; 8; <a:
+---+-+-----------+----+-----+-+-+--+
|+-+|2|+-------+-+|+--+|+---+|7|8|++|
||1|| ||+-----+|5|||++|||+-+|| | ||||
|+-+| |||+-+-+|| |||||||||6||| | |++|
| | ||||3|4||| |||++|||+-+|| | | |
| | |||+-+-+|| ||+--+|+---+| | | |
| | ||+-----+| || | | | | |
| | |+-------+-+| | | | | |
+---+-+-----------+----+-----+-+-+--+
flatten li
1 2 3 4 5 6 7 8
Alternative Solution:
The previous solution can be generalized to flatten the nesting and shape for a list of arbitrary values that include arrays of any rank:
flatten2 =: [: ; <@,S:0
Example:
]li2 =. (<1) ; 2; ((<3;4); 5 + i.3 4) ; ((<a:)) ; ((<(<17))) ; 18; 19; <a:
+---+-+---------------------+----+------+--+--+--+
|+-+|2|+-------+-----------+|+--+|+----+|18|19|++|
||1|| ||+-----+| 5 6 7 8|||++|||+--+|| | ||||
|+-+| |||+-+-+|| 9 10 11 12|||||||||17||| | |++|
| | ||||3|4|||13 14 15 16|||++|||+--+|| | | |
| | |||+-+-+|| ||+--+|+----+| | | |
| | ||+-----+| || | | | | |
| | |+-------+-----------+| | | | | |
+---+-+---------------------+----+------+--+--+--+
flatten2 li
1 2 3 4 5 6 7 8
flatten2 li2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Notes:
The primitive ; removes one level of nesting.
<S:0 takes an arbitrarily nested list and puts everything one level deep.
[: is glue, here.
We do not use ; by itself because it requires that all of the contents be the same type and nested items have a different type from unnested items.
We do not use ]S:0 (which puts everything zero levels deep) because it assembles its results as items of a list, which means that short items will be padded to be equal to the largest items, and that is not what we would want here (we do not want the empty item to be padded with a fill element).
[edit] Java
The flatten method was overloaded for better separation of concerns. On the first one you can pass any List and get it flat into a LinkedList implementation. On the other one you can pass any List implementation you like for both lists.
Note that both implementations can only put the result into type List<Object>. We cannot type-safely put the result into a generic type List<T> because there is no way to enforce that the original list contains elements of "type T or lists of elements which are T or further lists..."; there is no generic type parameter that will express that restriction. Since we must accept lists of any elements as an argument, we can only safely put them in a List<Object>.
Actual Workhorse code
import java.util.LinkedList;
import java.util.List;
public final class FlattenUtil {
public static List<Object> flatten(List<?> list) {
List<Object> retVal = new LinkedList<Object>();
flatten(list, retVal);
return retVal;
}
public static void flatten(List<?> fromTreeList, List<Object> toFlatList) {
for (Object item : fromTreeList) {
if (item instanceof List<?>) {
flatten((List<?>) item, toFlatList);
} else {
toFlatList.add(item);
}
}
}
}
Method showing population of the test List and usage of flatten method.
import static java.util.Arrays.asList;
import java.util.List;
public final class FlattenTestMain {
public static void main(String[] args) {
List<Object> treeList = a(a(1), 2, a(a(3, 4), 5), a(a(a())), a(a(a(6))), 7, 8, a());
List<Object> flatList = FlattenUtil.flatten(treeList);
System.out.println(treeList);
System.out.println("flatten: " + flatList);
}
private static List<Object> a(Object... a) {
return asList(a);
}
}
Output:
[[1], 2, [[3, 4], 5], [[[]]], [[[6]]], 7, 8, []] flatten: [1, 2, 3, 4, 5, 6, 7, 8]
[edit] JavaScript
function flatten(arr){
return arr.reduce(function(acc, val){
return acc.concat(val.constructor === Array ? flatten(val) : val);
},[]);
}
[edit] Julia
Julia auto-flattens nested arrays of this form
julia> t = [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]
8-element Int32 Array:
1
2
3
4
5
6
7
8
[edit] K
In K, join is: , and reduce/fold (called "over") is: /. With a monadic argument (as ,/ is), over repeats application until reaching a fixed-point.
So to flatten a list of arbitrary depth, you can join-over-over, or reduce a list with a function that reduces a list with a join function:
,//((1); 2; ((3;4); 5); ((())); (((6))); 7; 8; ())
[edit] Logtalk
flatten(List, Flatted) :-
flatten(List, [], Flatted).
flatten(Var, Tail, [Var| Tail]) :-
var(Var),
!.
flatten([], Flatted, Flatted) :-
!.
flatten([Head| Tail], List, Flatted) :-
!,
flatten(Tail, List, Aux),
flatten(Head, Aux, Flatted).
flatten(Head, Tail, [Head| Tail]).
[edit] Lua
function flatten(list)
if type(list) ~= "table" then return {list} end
local flat_list = {}
for _, elem in ipairs(list) do
for _, val in ipairs(flatten(elem)) do
flat_list[#flat_list + 1] = val
end
end
return flat_list
end
test_list = {{1}, 2, {{3,4}, 5}, {{{}}}, {{{6}}}, 7, 8, {}}
print(table.concat(flatten(test_list), ","))
[edit] Logo
to flatten :l
if not list? :l [output :l]
if empty? :l [output []]
output sentence flatten first :l flatten butfirst :l
end
; using a template iterator (map combining results into a sentence)
to flatten :l
output map.se [ifelse or not list? ? empty? ? [?] [flatten ?]] :l
end
make "a [[1] 2 [[3 4] 5] [[[]]] [[[6]]] 7 8 []]
show flatten :a
[edit] Mathematica
Flatten[{{1}, 2, {{3, 4}, 5}, {{{}}}, {{{6}}}, 7, 8, {}}]
[edit] Maxima
flatten([[[1, 2, 3], 4, [5, [6, 7]], 8], [[9, 10], 11], 12]);
/* [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12] */
[edit] Mirah
import java.util.ArrayList
import java.util.List
import java.util.Collection
def flatten(list: Collection)
flatten(list, ArrayList.new)
end
def flatten(source: Collection, result: List)
source.each do |x|
if x.kind_of?(Collection)
flatten(Collection(x), result)
else
result.add(x)
result # if branches must return same type
end
end
result
end
# creating a list-of-list-of-list fails currently, so constructor calls are needed
source = [[1], 2, [[3, 4], 5], [[ArrayList.new]], [[[6]]], 7, 8, ArrayList.new]
puts flatten(source)
[edit] NewLISP
> (flat '((1) 2 ((3 4) 5) ((())) (((6))) 7 8 ()))
(1 2 3 4 5 6 7 8)
[edit] Objective-C
and#import <Foundation/Foundation.h>
@interface NSArray (FlattenExt)
-(NSArray *)flatten;
@end
@implementation NSArray (FlattenExt)
-(NSArray *)flatten
{
NSMutableArray *r = [NSMutableArray array];
NSEnumerator *en = [self objectEnumerator];
id o;
while ( (o = [en nextObject]) ) {
if ( [o isKindOfClass: [NSArray class]] )
[r addObjectsFromArray: [o flatten]];
else
[r addObject: o];
}
return [NSArray arrayWithArray: r];
}
@end
int main()
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
NSArray *p = [NSArray
arrayWithObjects:
[NSArray arrayWithObjects: [NSNumber numberWithInt: 1], nil],
[NSNumber numberWithInt: 2],
[NSArray arrayWithObjects:
[NSArray arrayWithObjects: [NSNumber numberWithInt: 3],
[NSNumber numberWithInt: 4], nil],
[NSNumber numberWithInt: 5], nil],
[NSArray arrayWithObjects:
[NSArray arrayWithObjects:
[NSArray arrayWithObjects: nil], nil], nil],
[NSArray arrayWithObjects:
[NSArray arrayWithObjects:
[NSArray arrayWithObjects:
[NSNumber numberWithInt: 6], nil], nil], nil],
[NSNumber numberWithInt: 7],
[NSNumber numberWithInt: 8],
[NSArray arrayWithObjects: nil], nil];
NSArray *f = [p flatten];
NSEnumerator *e = [f objectEnumerator];
id o;
while( (o = [e nextObject]) )
{
NSLog(@"%@", o);
}
[pool drain];
return 0;
}
An alternative solution
#import <Foundation/Foundation.h>
@interface NSArray (FlattenExt)
@property (nonatomic, readonly) NSArray *flattened;
@end
@implementation NSArray (FlattenExt)
-(NSArray *) flattened {
NSMutableArray *flattened = [[NSMutableArray alloc] initWithCapacity:self.count];
for (id object in self) {
if ([object isKindOfClass:[NSArray class]])
[flattened addObjectsFromArray:((NSArray *)object).flattened];
else
[flattened addObject:object];
}
return [flattened autorelease];
}
@end
int main() {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
NSArray *unflattened = [NSArray arrayWithObjects:[NSArray arrayWithObject:[NSNumber numberWithInteger:1]],
[NSNumber numberWithInteger:2],
[NSArray arrayWithObjects:[NSArray arrayWithObjects:[NSNumber numberWithInteger:3], [NSNumber numberWithInteger:4], nil],
[NSNumber numberWithInteger:5], nil],
[NSArray arrayWithObject:[NSArray arrayWithObject:[NSArray array]]],
[NSArray arrayWithObject:[NSArray arrayWithObject:[NSArray arrayWithObject:[NSNumber numberWithInteger:6]]]],
[NSNumber numberWithInteger:7],
[NSNumber numberWithInteger:8],
[NSArray array], nil];
for (id object in unflattened.flattened)
NSLog(@"%@", object);
[pool drain];
return 0;
}
[edit] OCaml
# let flatten = List.concat ;;
val flatten : 'a list list -> 'a list = <fun>
# let li = [[1]; 2; [[3;4]; 5]; [[[]]]; [[[6]]]; 7; 8; []] ;;
^^^
Error: This expression has type int but is here used with type int list
# (* use another data which can be accepted by the type system *)
flatten [[1]; [2; 3; 4]; []; [5; 6]; [7]; [8]] ;;
- : int list = [1; 2; 3; 4; 5; 6; 7; 8]
Since OCaml is statically typed, it is not possible to have a value that could be both a list and a non-list. Instead, we can use an algebraic datatype:
# type 'a tree = Leaf of 'a | Node of 'a tree list ;;
type 'a tree = Leaf of 'a | Node of 'a tree list
# let rec flatten = function
Leaf x -> [x]
| Node xs -> List.concat (List.map flatten xs) ;;
val flatten : 'a tree -> 'a list = <fun>
# flatten (Node [Node [Leaf 1]; Leaf 2; Node [Node [Leaf 3; Leaf 4]; Leaf 5]; Node [Node [Node []]]; Node [Node [Node [Leaf 6]]]; Leaf 7; Leaf 8; Node []]) ;;
- : int list = [1; 2; 3; 4; 5; 6; 7; 8]
[edit] Oz
Oz has a standard library function "Flatten":
{Show {Flatten [[1] 2 [[3 4] 5] [[nil]] [[[6]]] 7 8 nil]}}
A simple, non-optimized implementation could look like this:
fun {Flatten2 Xs}
case Xs of nil then nil
[] X|Xr then
{Append {Flatten2 X} {Flatten2 Xr}}
else [Xs]
end
end
[edit] ooRexx
sub1 = .array~of(1)
sub2 = .array~of(3, 4)
sub3 = .array~of(sub2, 5)
sub4 = .array~of(.array~of(.array~new))
sub5 = .array~of(.array~of(.array~of(6)))
sub6 = .array~new
-- final list construction
list = .array~of(sub1, 2, sub3, sub4, sub5, 7, 8, sub6)
-- flatten
flatlist = flattenList(list)
say "["flatlist~toString("line", ", ")"]"
::routine flattenList
use arg list
-- we could use a list or queue, but let's just use an array
accumulator = .array~new
-- now go to the recursive processing version
call flattenSublist list, accumulator
return accumulator
::routine flattenSublist
use arg list, accumulator
-- ask for the items explicitly, since this will allow
-- us to flatten indexed collections as well
do item over list~allItems
-- if the object is some sort of collection, flatten this out rather
-- than add to the accumulator
if item~isA(.collection) then call flattenSublist item, accumulator
else accumulator~append(item)
end
[edit] PARI/GP
flatten(v)={
my(u=[]);
for(i=1,#v,
u=concat(u,if(type(v[i])=="t_VEC",flatten(v[i]),v[i]))
);
u
};
[edit] Perl
sub flatten {
map { ref eq 'ARRAY' ? flatten(@$_) : $_ } @_
}
my @lst = ([1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []);
print flatten(@lst), "\n";
[edit] Perl 6
multi flatten (@a) { map { flatten $^x }, @a }
multi flatten ($x) { $x }
[edit] PHP
/* Note: This code is only for PHP 4.
It won't work on PHP 5 due to the change in behavior of array_merge(). */
while (array_filter($lst, 'is_array'))
$lst = call_user_func_array('array_merge', $lst);
Explanation: while $lst has any elements which are themselves arrays (i.e. $lst is not flat), we merge the elements all together (in PHP 4, array_merge() treated non-array arguments as if they were 1-element arrays; PHP 5 array_merge() no longer allows non-array arguments.), thus flattening the top level of any embedded arrays. Repeat this process until the array is flat.
[edit] Recursive
<?phpAlternatively:
function flatten($ary) {
$result = array();
foreach ($ary as $x) {
if (is_array($x))
// append flatten($x) onto $result
array_splice($result, count($result), 0, flatten($x));
else
$result[] = $x;
}
return $result;
}
$lst = array(array(1), 2, array(array(3, 4), 5), array(array(array())), array(array(array(6))), 7, 8, array());
var_dump(flatten($lst));
?>
<?php
function flatten($ary) {
$result = array();
array_walk_recursive($ary, function($x, $k) use (&$result) { $result[] = $x; });
return $result;
}
$lst = array(array(1), 2, array(array(3, 4), 5), array(array(array())), array(array(array(6))), 7, 8, array());
var_dump(flatten($lst));
?>
<?php
function flatten_helper($x, $k, $obj) {
$obj->flattened[] = $x;
}
function flatten($ary) {
$obj = (object)array('flattened' => array());
array_walk_recursive($ary, 'flatten_helper', $obj);
return $obj->flattened;
}
$lst = array(array(1), 2, array(array(3, 4), 5), array(array(array())), array(array(array(6))), 7, 8, array());
var_dump(flatten($lst));
?>
Using the standard library (warning: objects will also be flattened by this method):
<?php
$lst = array(array(1), 2, array(array(3, 4), 5), array(array(array())), array(array(array(6))), 7, 8, array());
$result = iterator_to_array(new RecursiveIteratorIterator(new RecursiveArrayIterator($lst)), false);
var_dump($result);
?>
[edit] Non-recursive
Function flat is iterative and flattens the array in-place.
<?php
function flat(&$ary) { // argument must be by reference or array will just be copied
for ($i = 0; $i < count($ary); $i++) {
while (is_array($ary[$i])) {
array_splice($ary, $i, 1, $ary[$i]);
}
}
}
$lst = array(array(1), 2, array(array(3, 4), 5), array(array(array())), array(array(array(6))), 7, 8, array());
flat($lst);
var_dump($lst);
?>
[edit] PicoLisp
(de flatten (X)
(make # Build a list
(recur (X) # recursively over 'X'
(if (atom X)
(link X) # Put atoms into the result
(mapc recurse X) ) ) ) ) # or recurse on sub-lists
or a more succint way using fish:
(de flatten (X)
(fish atom X) )
[edit] Pike
There's a built-in function called Array.flatten() which does this, but here's a custom function:
array flatten(array a) {
array r = ({ });
foreach (a, mixed n) {
if (arrayp(n)) r += flatten(n);
else r += ({ n });
}
return r;
}
[edit] PL/I
list = translate (list, ' ', '[]' );
list = '[' || list || ']';
/* the above will erroneously return:
[ 1 , 2, 3,4 , 5 , , 6 , 7, 8, ]
*/
[edit] PostScript
/flatten {
/.f {{type /arraytype eq} {{.f} map aload pop} ift}.
[exch .f]
}.
[[1] 2 [[3 4] 5] [[[]]] [[[6]]] 7 8 []] flatten
[edit] Prolog
flatten(List, FlatList) :-
flatten(List, [], FlatList).
flatten(Var, T, [Var|T]) :-
var(Var), !.
flatten([], T, T) :- !.
flatten([H|T], TailList, List) :- !,
flatten(H, FlatTail, List),
flatten(T, TailList, FlatTail).
flatten(NonList, T, [NonList|T]).
[edit] PureBasic
Structure RCList
Value.i
List A.RCList()
EndStructure
Procedure Flatten(List A.RCList())
ResetList(A())
While NextElement(A())
With A()
If \Value
Continue
Else
ResetList(\A())
While NextElement(\A())
If \A()\Value: A()\Value=\A()\Value: EndIf
Wend
EndIf
While ListSize(\A()): DeleteElement(\A()): Wend
If Not \Value: DeleteElement(A()): EndIf
EndWith
Wend
EndProcedure
Set up the MD-List & test the Flattening procedure.
;- Set up two lists, one multi dimensional and one 1-D.
NewList A.RCList()
;- Create a deep list
With A()
AddElement(A()): AddElement(\A()): AddElement(\A()): \A()\Value=1
AddElement(A()): A()\Value=2
AddElement(A()): AddElement(\A()): \A()\Value=3
AddElement(\A()): \A()\Value=4
AddElement(A()): AddElement(\A()): \A()\Value=5
AddElement(A()): AddElement(\A()): AddElement(\A()): AddElement(\A())
AddElement(A()): AddElement(\A()): AddElement(\A()): \A()\Value=6
AddElement(A()): A()\Value=7
AddElement(A()): A()\Value=8
AddElement(A()): AddElement(\A()): AddElement(\A())
EndWith
Flatten(A())
;- Present the result
If OpenConsole()
Print("Flatten: [")
ForEach A()
Print(Str(A()\Value))
If ListIndex(A())<(ListSize(A())-1)
Print(", ")
Else
PrintN("]")
EndIf
Next
Print(#CRLF$+"Press ENTER to quit"): Input()
EndIf
Flatten: [1, 2, 4, 5, 6, 7, 8]
[edit] Python
[edit] Recursive
Function flatten is recursive and preserves its argument:
>>> def flatten(lst):
return sum( ([x] if not isinstance(x, list) else flatten(x)
for x in lst), [] )
>>> lst = [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]
>>> flatten(lst)
[1, 2, 3, 4, 5, 6, 7, 8]
[edit] Non-recursive
Function flat is iterative and flattens the list in-place. It follows the Python idiom of returning None when acting in-place:
>>> def flat(lst):
i=0
while i<len(lst):
while True:
try:
lst[i:i+1] = lst[i]
except (TypeError, IndexError):
break
i += 1
>>> lst = [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]
>>> flat(lst)
>>> lst
[1, 2, 3, 4, 5, 6, 7, 8]
[edit] Generative
This method shows a solution using Python generators.
flatten is a generator that yields the non-list values of its input in order.
In this case, the generator is converted back to a list before printing.
>>> def flatten(lst):
for x in lst:
if isinstance(x, list):
for x in flatten(x):
yield x
else:
yield x
>>>lst = [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]
>>>print list(flatten(lst))
[1, 2, 3, 4, 5, 6, 7, 8]
[edit] R
x <- list(list(1), 2, list(list(3, 4), 5), list(list(list())), list(list(list(6))), 7, 8, list())
unlist(x)
[edit] Racket
Racket has a built-in flatten function:
#lang racket
(flatten '(1 (2 (3 4 5) (6 7)) 8 9))
outputs:
'(1 2 3 4 5 6 7 8 9)
or, writing it explicitly with the same result:
#lang racket
(define (flatten l)
(cond [(empty? l) null]
[(not (list? l)) (list l)]
[else (append (flatten (first l)) (flatten (rest l)))]))
(flatten '(1 (2 (3 4 5) (6 7)) 8 9))
[edit] REBOL
Sample:
flatten: func [
"Flatten the block in place."
block [any-block!]
][
parse block [
any [block: any-block! (change/part block first block 1) :block | skip]
]
head block
]
>> flatten [[1] 2 [[3 4] 5] [[[]]] [[[6]]] 7 8 []] == [1 2 3 4 5 6 7 8]
[edit] REXX
[edit] version 1
/*REXX program to demonstrate how to flatten a list. */
y = '[[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]'
z = '['changestr(' ',space(translate(y,,'[,]')),", ")']'
say ' input =' y
say 'output =' z
/*stick a fork in it, we're done.*/
Some older REXXes don't have a changestr bif, so one is included here ──► CHANGESTR.REX.
output
input = [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []] output = [1, 2, 3, 4, 5, 6, 7, 8]
[edit] version 2
/*REXX program to demonstrate how to flatten a list. */
y = '[[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]'
z=translate(y,,'[,]') /*change brackets & commas to blanks*/
z=space(z) /*remove extraneous blanks*/
z=changestr(' ',z,", ") /*change blanks to "comma blank"*/
z='['z"]" /*add brackets*/
say ' input =' y
say 'output =' z
/*stick a fork in it, we're done.*/
output is the same as the 1st version.
[edit] Ruby
flatten is a built-in method of Arrays
flat = [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []].flatten
p flat # => [1, 2, 3, 4, 5, 6, 7, 8]
[edit] Run BASIC
latten$ = "[[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8 []]"Output:
i = instr(flatten$,"[")
while i > 0
flatten$ = left$(flatten$,i-1) + mid$(flatten$,i+1)
i = instr(flatten$,"]")
flatten$ = left$(flatten$,i-1) + mid$(flatten$,i+1)
i = instr(flatten$," ")
flatten$ = left$(flatten$,i-1) + mid$(flatten$,i+1)
i = instr(flatten$,",,")
flatten$ = left$(flatten$,i-1) + mid$(flatten$,i+1)
i = instr(flatten$,"[")
wend
print flatten$
1,2,3,4,5,6,7,8
[edit] S-lang
define flatten ();
define flatten (list) {
variable item,
retval,
val;
if (typeof(list) != List_Type) {
retval = list;
} else {
retval = {};
foreach item (list) {
foreach val (flatten(item)) {
list_append(retval, val);
}
}
}
return retval;
}
Sample:
slsh> variable data = {{1}, 2, {{3,4}, 5}, {{{}}}, {{{6}}}, 7, 8, {}},
result = flatten(data);
slsh> print(result);
{
1
2
3
4
5
6
7
8
}
[edit] Scala
def flatList(l: List[_]): List[Any] = l match {
case Nil => Nil
case (head: List[_]) :: tail => flatList(head) ::: flatList(tail)
case head :: tail => head :: flatList(tail)
}
Sample:
scala> List(List(1), 2, List(List(3, 4), 5), List(List(List())), List(List(List(6))), 7, 8, List()) res10: List[Any] = List(List(1), 2, List(List(3, 4), 5), List(List(List())), List(List(List(6))), 7, 8, List()) scala> flatList(res10) res12: List[Any] = List(1, 2, 3, 4, 5, 6, 7, 8)
[edit] Scheme
> (define (flatten x)
(cond ((null? x) '())
((not (pair? x)) (list x))
(else (append (flatten (car x))
(flatten (cdr x))))))
> (flatten '((1) 2 ((3 4) 5) ((())) (((6))) 7 8 ()))
(1 2 3 4 5 6 7 8)
[edit] Slate
s@(Sequence traits) flatten
[
[| :out | s flattenOn: out] writingAs: s
].
s@(Sequence traits) flattenOn: w@(WriteStream traits)
[
s do: [| :value |
(value is: s)
ifTrue: [value flattenOn: w]
ifFalse: [w nextPut: value]].
].
[edit] Smalltalk
OrderedCollection extend [
flatten [ |f|
f := OrderedCollection new.
self do: [ :i |
i isNumber
ifTrue: [ f add: i ]
ifFalse: [ |t|
t := (OrderedCollection withAll: i) flatten.
f addAll: t
]
].
^ f
]
].
|list|
list := OrderedCollection
withAll: { {1} . 2 . { {3 . 4} . 5 } .
{{{}}} . {{{6}}} . 7 . 8 . {} }.
(list flatten) printNl.
[edit] Suneido
ob = [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]
ob.Flatten()
Output:
#(1, 2, 3, 4, 5, 6, 7, 8)
[edit] Tcl
proc flatten list {
for {set old {}} {$old ne $list} {} {
set old $list
set list [join $list]
}
return $list
}
puts [flatten {{1} 2 {{3 4} 5} {{{}}} {{{6}}} 7 8 {}}]
# ===> 1 2 3 4 5 6 7 8
Note that because lists are not syntactically distinct from strings, it is probably a mistake to use this procedure with real (especially non-numeric) data. Also note that there are no parentheses around the outside of the list when printed; this is just a feature of how Tcl regards lists, and the value is a proper list (it can be indexed into with lindex, iterated over with foreach, etc.)
Another implementation that's slightly more terse:
proc flatten {data} {
while { $data != [set data [join $data]] } { }
return $data
}
puts [flatten {{1} 2 {{3 4} 5} {{{}}} {{{6}}} 7 8 {}}]
# ===> 1 2 3 4 5 6 7 8
[edit] TI-89 BASIC
There is no nesting of lists or other data structures in TI-89 BASIC, short of using variable names as pointers.
[edit] Trith
[[1] 2 [[3 4] 5] [[[]]] [[[6]]] 7 8 []] flatten
[edit] TXR
An important builtin.
@(bind foo ((1) 2 ((3 4) 5) ((())) (((6))) 7 8 ()))
@(bind bar foo)
@(flatten bar)
Run:
$ txr -a 5 flatten.txr # show variable bindings in array notation to depth 5 foo[0][0]="1" foo[1]="2" foo[2][0][0]="3" foo[2][0][1]="4" foo[2][1]="5" foo[4][0][0][0]="6" foo[5]="7" foo[6]="8" bar[0]="1" bar[1]="2" bar[2]="3" bar[3]="4" bar[4]="5" bar[5]="6" bar[6]="7" bar[7]="8"
[edit] VBScript
Working on embedded arrays as that's about the closest we get to lists.
[edit] Implementation
class flattener
dim separator
sub class_initialize
separator = ","
end sub
private function makeflat( a )
dim i
dim res
for i = lbound( a ) to ubound( a )
if isarray( a( i ) ) then
res = res & makeflat( a( i ) )
else
res = res & a( i ) & separator
end if
next
makeflat = res
end function
public function flatten( a )
dim res
res = makeflat( a )
res = left( res, len( res ) - len(separator))
res = split( res, separator )
flatten = res
end function
public property let itemSeparator( c )
separator = c
end property
end class
[edit] Invocation
dim flat
set flat = new flattener
flat.itemSeparator = "~"
wscript.echo join( flat.flatten( array( array( 1 ),2,array(array(3,4),5),array(array(array())),array(array(array(6))),7,8,array())), "!")
[edit] Output
1!2!3!4!5!6!7!8
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