Apply a callback to an array
You are encouraged to solve this task according to the task description, using any language you may know.
Ada
Tested With:
- Gnat GPL 2005
- Amd-64bit-3500+-WinXP
with Ada.Text_Io;
with Ada.Integer_text_IO;
procedure Call_Back_Example is
-- Purpose: Apply a callback to an array
-- Output: Prints the squares of an integer array to the console
-- Define the callback procedure
procedure Display(Location : Positive; Value : Integer) is
begin
Ada.Text_Io.Put("array(");
Ada.Integer_Text_Io.Put(Item => Location, Width => 1);
Ada.Text_Io.Put(") = ");
Ada.Integer_Text_Io.Put(Item => Value * Value, Width => 1);
Ada.Text_Io.New_Line;
end Display;
-- Define an access type matching the signature of the callback procedure
type Call_Back_Access is access procedure(L : Positive; V : Integer);
-- Define an unconstrained array type
type Value_Array is array(Positive range <>) of Integer;
-- Define the procedure performing the callback
procedure Map(Values : Value_Array; Worker : Call_Back_Access) is
begin
for I in Values'range loop
Worker(I, Values(I));
end loop;
end Map;
-- Define and initialize the actual array
Sample : Value_Array := (5,4,3,2,1);
begin
Map(Sample, Display'access);
end Call_Back_Example;
C
Tested With:
- GCC 3.3.6
- i686-pc-linux-gnu
- GCC 3.4.6
- i686-pc-linux-gnu
- GCC 4.0.3
- i686-pc-linux-gnu
- GCC 4.1.1
- i686-pc-linux-gnu
- powerpc-unknown-linux-gnu
- TCC 0.9.23
- i686-pc-linux-gnu
- ICC 9.1
- i686-pc-linux-gnu
callback.h
#ifndef __CALLBACK_H #define __CALLBACK_H /* * By declaring the function in a separate file, we allow * it to be used by other source files. * * It also stops ICC from complaining. * * If you don't want to use it outside of callback.c, this * file can be removed, provided the static keyword is prepended * to the definition. */ void map(int* array, int len, void(*callback)(int,int)); #endif
callback.c
#include <stdio.h>
#include "callback.h"
/*
* We don't need this function outside of this file, so
* we declare it static.
*/
static void callbackFunction(int location, int value)
{
printf("array[%d] = %d\n", location, value);
}
void map(int* array, int len, void(*callback)(int,int))
{
int i;
for(i = 0; i < len; i++)
{
callback(i, array[i]);
}
}
int main()
{
int array[] = { 1, 2, 3, 4 };
map(array, 4, callbackFunction);
return 0;
}
Output
array[0] = 1 array[1] = 2 array[2] = 3 array[3] = 4
C#
Platform: .NET
Language Version: 2.0+
Compiler: Visual C# 2005
using System;
static class Program
{
// Purpose: Apply a callback (or anonymous method) to an Array
// Output: Prints the squares of an int array to the console.
// Compiler: Visual Studio 2005
// Framework: .net 2
[STAThread]
public static void Main()
{
int[] intArray = { 1, 2, 3, 4, 5 };
// Using a callback,
Console.WriteLine("Printing squares using a callback:");
Array.ForEach<int>(intArray, PrintSquare);
// or using an anonymous method:
Console.WriteLine("Printing squares using an anonymous method:");
Array.ForEach<int>
(
intArray,
delegate(int value)
{
Console.WriteLine(value * value);
});
}
public static void PrintSquare(int value)
{
Console.WriteLine(value * value);
}
}
C++
Compiler: GNU Compiler Collection 4.1.1
Using c-style array
#include <iostream> //cout for printing
#include <algorithm> //for_each defined here
//create the function (print the square)
void print_square(int i) {
std::cout << i*i << " ";
}
int main() {
//create the array
int ary[]={1,2,3,4,5};
//stl for_each
std::for_each(ary,ary+5,print_square);
return 0;
}
//prints 1 4 9 16 25
#include <iostream> //cout for printing
#include <algorithm> //for_each defined here
#include <vector> //stl vector class
//create the function (print the square)
void print_square(int i) {
std::cout << i*i << " ";
}
int main() {
//create the array
std::vector<int> ary;
ary.push_back(1);
ary.push_back(2);
ary.push_back(3);
ary.push_back(4);
ary.push_back(5);
//stl for_each
std::for_each(ary.begin(),ary.end(),print_square);
return 0;
}
//prints 1 4 9 16 25
More tricky with binary function
#include <iostream> //cout for printing
#include <algorithm> //for_each defined here
#include <vector> //stl vector class
#include <functional> //bind and ptr_fun
//create a binary function (print any two arguments together)
template<class type1,class type2>
void print_juxtaposed(type1 x, type2 y) {
std::cout << x << y;
}
int main() {
//create the array
std::vector<int> ary;
ary.push_back(1);
ary.push_back(2);
ary.push_back(3);
ary.push_back(4);
ary.push_back(5);
//stl for_each, using binder and adaptable unary function
std::for_each(ary.begin(),ary.end(),std::bind2nd(std::ptr_fun(print_juxtaposed<int,std::string>),"x "));
return 0;
}
//prints 1x 2x 3x 4x 5x
Using Boost.Lambda
using namespace std; using namespace boost::lambda; vector<int> ary(10); int i = 0; for_each(ary.begin(), ary.end(), _1 = ++var(i)); // init array transform(ary.begin(), ary.end(), ostream_iterator<int>(cout, " "), _1 * _1); // square and output
Clean
Define a function and an initial (unboxed) array.
square x = x * x
values :: {#Int}
values = {x \\ x <- [1 .. 10]}
One can easily define a map for arrays, which is overloaded and works for all kinds of arrays (lazy, strict, unboxed).
mapArray f array = {f x \\ x <-: array}
Apply the function to the initial array (using a comprehension) and print result.
Start :: {#Int}
Start = mapArray square values
Common Lisp
Imperative: print 1, 2, 3, 4 and 5:
(map nil #'print #(1 2 3 4 5))
Functional: collect squares into new vector that is returned:
(defun square (x) (* x x)) (map 'vector #'square #(1 2 3 4 5))
Destructive, like the Javascript example; add 1 to every slot of vector *a*:
(defvar *a* (vector 1 2 3)) (map-into *a* #'1+ *a*)
E
def array := [1,2,3,4,5]
def square(value) {
return value * value
}
Example of builtin iteration:
def callback(index, value) {
println(`Item $index is $value.`)
}
array.iterate(callback)
There is no builtin map function yet. the following is one of the ways one could be implemented, returning a plain list (which is usually an array in implementation).
def map(func, collection) {
def output := [].diverge()
for item in collection {
output.push(func(item))
}
return output.snapshot()
}
println(map(square, array))
Forth
This is a word that will call a given function on each cell in an array.
: map ( addr n fn -- ) -rot cells bounds do i @ over execute i ! cell +loop ;
Example usage:
create data 1 , 2 , 3 , 4 , 5 , data 5 ' 1+ map \ adds one to each element of data
Fortran
program test
C
C-- Declare array:
integer a(5)
C
C-- Fill it with Data
data a /45,22,67,87,98/
C
C-- Do something with all elements (in this case: print their squares)
do i=1,5
print *,a(i)*a(i)
end do
C
end
FP
Interpreter : "fp"
{square * . [id, id]}
& square: <1,2,3,4,5>
Haskell
Interpreter : GHCi
Compiler : GHC
let square x = x*x let values = [1..10] map square values
Using list comprehension to generate a list of the squared values
[square x | x <- values]
Using function composition to create a function that will print the squares of a list
let printSquares = putStr.unlines.map (show.square) printSquares values
IDL
Hard to come up with an example that isn't completely contrived. IDL doesn't really distinguish between a scalar and an array; thus
b = a^3
will yield a scalar if a is scalar or a vector if a is a vector or an n-dimensional array is a is an n-dimensional array
JavaScript
Portable technique:
function map(a, func) {
for (var i in a)
a[i] = func(a[i]);
}
var a = [1, 2, 3, 4, 5];
map(a, function(v) { return v * v; });
With the BeyondJS library:
var a = (1).to(10).collect(Math.pow.curry(undefined,2));
With Firefox 2.0:
function cube(num) {
return Math.pow(num, 3);
}
var numbers = [1, 2, 3, 4, 5];
//get results of calling cube on every element
var cubes1 = numbers.map(cube);
//display each result in a separate dialog
cubes1.forEach(alert);
//array comprehension
var cubes2 = [cube(n) for each (n in numbers)];
var cubes3 = [n * n * n for each (n in numbers)];
Lua
Say we have an array:
myArray = {1, 2, 3, 4, 5}
A map function for this would be
map = function(f, data)
local result = {}
for k,v in ipairs(data) do
result[k] = f(v)
end
return result
end
Together with our array and and a square function this yields:
myFunc = function(x) return x*x end print(unpack( map(myFunc, myArray) )) --> 1 4 9 16 25
If you used pairs() instead of ipairs(), this would even work on a hash table in general.
OCaml
This function is part of the standard library:
Array.map
Usage example:
let square x = x * x;; let values = Array.init 10 ((+) 1);; Array.map square values;;
Perl
# create array my @a = (1, 2, 3, 4, 5);
# create callback function
sub mycallback {
return 2 * shift;
}
# use array indexing
my $i;
for ($i = 0; $i < scalar @a; $i++) {
print "mycallback($a[$i]) = ", mycallback($a[$i]), "\n";
}
# using foreach
foreach my $x (@a) {
print "mycallback($x) = ", mycallback($x), "\n";
}
# using map (useful for transforming an array) my @b = map mycallback($_), @a; # @b is now (2, 4, 6, 8, 10)
# and the same using an anonymous function
my @c = map { $_ * 2 } @a; # @c is now (2, 4, 6, 8, 10)
# use a callback stored in a variable
my $func = \&mycallback;
my @d = map &{$func}($_), @a; # @d is now (2, 4, 6, 8, 10)
PHP
function cube($n)
{
return($n * $n * $n);
}
$a = array(1, 2, 3, 4, 5);
$b = array_map("cube", $a);
print_r($b);
PL/SQL
Interpreter : Oracle compiler
set serveroutput on
declare
type myarray is table of number index by binary_integer;
x myarray;
i pls_integer;
begin
-- populate array
for i in 1..5 loop
x(i) := i;
end loop;
i :=0;
-- square array
loop
i := i + 1;
begin
x(i) := x(i)*x(i);
dbms_output.put_line(x(i));
exception
when no_data_found then exit;
end;
end loop;
end;
/
Pop11
;;; Define a procedure
define proc(x);
printf(x*x, '%p,');
enddefine;
;;; Create array
lvars ar = { 1 2 3 4 5};
;;; Apply procedure to array appdata(ar, proc);
If one wants to create a new array consisting of transformed values then procedure mapdata may be more convenient.
Python
def square(n):
return n * n
numbers = [1, 3, 5, 7]
squares1 = [square(n) for n in numbers] # list comprehension
squares2 = map(square, numbers) # discouraged nowadays
squares3 = [n * n for n in numbers] # no need for a function,
# anonymous or otherwise
isquares = (n * n for n in numbers) # iterator, lazy
Ruby
# You could use a traditional "for i in arr" approach like below:
for i in [1,2,3,4,5] do
puts i**2
end
# Or you could the more preferred ruby way of an iterator (which is borrowed from SmallTalk)
[1,2,3,4,5].each{ |i| puts i**2 }
# To create a new array of each value squared
[1,2,3,4,5].map{ |i| i**2 }
Scala
val l = List(1,2,3,4)
l.foreach {i => Console.println(i)}
Same for an array
val a = Array(1,2,3,4)
a.foreach {i => Console.println(i)}
// Or for an externally defined function
def doSomething(in: int) = {Console.println("Doing something with "+in)}
l.foreach(doSomething)
There is also a for syntax, which is internally rewritten to call foreach. A foreach method must be define on a
for(val i <- a) Console.println(i)
It is also possible to apply a function on each item of an list to get a new list (same on array and most collections)
val squares = l.map{i => i * i} //returns List(1,4,9,16)
Or the equivalent for syntax, with the additional keyword yield, map is called instead of foreach
val squares = for (val i <- l) yield i * i
Scheme
(define (square n) (* n n)) (define x #(1 2 3 4 5)) (map square (vector->list x))
A single-line variation
(map (lambda (n) (* n n)) '(1 2 3 4 5))
For completeness, the map function (which is R5RS standard) can be coded as follows:
(define (map f L)
(if (null? L)
L
(cons (f (car L)) (map f (cdr L)))))
Smalltalk
| anArray | anArray = #( 1 2 3 4 5 ) anArray do: [ :x | Transcript nextPut: x * x ]
Tcl
If I wanted to call "myfunc" on each element of dat and dat were a list:
foreach var $dat { myfunc $var }
if dat were an array, however:
foreach var [array names dat] { myfunc $dat($var) }
Toka
( array count function -- )
{
variable| array fn |
[ i 1- array @ ] is I
[ fn ! swap array ! [ I get-element fn @ invoke I put-element ] +iterate ]
} is map-array
( Build an array )
5 cells is-array a
10 0 a put-element
11 1 a put-element
12 2 a put-element
13 3 a put-element
14 4 a put-element
( Add 1 to each item in the array )
a 5 ` 1+ map-array