CODEWITHSUNDEEP
php
sg5523
sg5523

Reputation: 33

How do I use array_map to also specify keys?

Using the canonical PHPdoc example, this code:

<?php
function cube($n)
{
    return($n * $n * $n);
}

$a = array( 3, 4, 5);
$b = array_map("cube", $a);
print_r($b);
?>

outputs

Array

(
    [0] => 27
    [1] => 64
    [2] => 125
)

But what I really want it to output is something along these lines: Array

(
    [3] => 27
    [4] => 64
    [5] => 125
)

That is, I want the array_map to use the same keys as in the original array. Is there any way to do that? Thanks!

Upvotes: 3

Views: 206

Answers (4)

Orangepill
Orangepill

Reputation: 24645

While you can't use array_map to rewrite keys you can use array_reduce with a closure (PHP 5.3+)

<?php
function cube($n){
    return $n*$n*$n;
}

$data = array(3,4,5);
$function = "cube";
$res = array_reduce($data, function(&$result = array(), $item) use($function){

   if (!is_array($result)){
    $result = array();
   };
   $result[$item] = $function($item);
   return $result;
});

print_r($res);

The output is 

Array
(
    [3] => 27
    [4] => 64
    [5] => 125
)

Upvotes: 2

jcbwlkr
jcbwlkr

Reputation: 7999

Instead of using array_map which returns a modified array you could use array_walk which can modify the given array. Note that the callback used by array_walk needs to accept its arguments by reference if you intend to change them

<?php    
$cube = function(&$x) {
    // Modify $x by reference
    $x = pow($x, 3);
};

$data = array(
    3 => 3,
    4 => 4,
    5 => 5
);

array_walk($data, $cube);

print_r($data);

This prints

Array
(
    [3] => 27
    [4] => 64
    [5] => 125
)

Upvotes: 1

deceze
deceze

Reputation: 522085

Not using array_map, it explicitly only maps values. But this'll do:

array_combine($a, array_map('cube', $a))

Upvotes: 1

nickb
nickb

Reputation: 59699

Use array_combine():

$b = array_combine( $a, array_map("cube", $a));

You can see from this demo that it produces:

Array
(
    [3] => 27
    [4] => 64
    [5] => 125
)

Upvotes: 3

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