Apply a callback to an array
You are encouraged to solve this task according to the task description, using any language you may know.
Create a generic mapping function that applies a callback to elements in a list:
C#
Platform: .NET Language Version: 2.0+
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
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
JavaScript
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; });
// JavaScript with BeyondJS
var a = (1).to(10).collect(Math.pow.curry(undefined,2));
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($x) , "\n";
}
# using map (useful for transforming the array )
my @b = map mycallback($_), @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; /
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] # best - doesn't need a function, anonymous or otherwise
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 }
Scheme
(define (square n) (* n n)) (define x '(1 2 3 4 5)) (map square x)
Smalltalk
| anArray | anArray = #( 1 2 3 4 5 ) anArray do: [ :x | Transcript nextPut: x * x ]