Flipping the keys and constructing the values from another array

Question

I have the following two arrays:

$a1 = [56,60];
$a2 = [60 => 'aa', 61 => 'bb', 62 => 'cc', 63 => 'dd'];

I'm trying to apply array_map to construct a new array that would look like this:

Array
(
    [56] =>        
    [60] => aa
)

Basically what I need is to go through the first array, if I find it in the second array, I'll grab its corresponding value, otherwise, set it to an empty string. Is array_map the best way to go about this?

Answer 1

A simple loop seems easiest to me, using array_key_exists()

$a1 = [56,60];
$a2 = [60 => 'aa',61 => 'bb',62 => 'cc',63 => 'dd'];

$new = [];

foreach ( $a1 as $key )  {
    if ( array_key_exists($key, $a2) ) {
        $new[$key] = $a2[$key];
    }
}

print_r($new);

RESULT

Array
(
    [60] => aa
)

Or if you really want a blank occurance, this would work

$a1 = [56,60];
$a2 = [60 => 'aa',61 => 'bb',62 => 'cc',63 => 'dd'];

$new = [];

foreach ( $a1 as $key )  {
    $new[$key] = array_key_exists($key, $a2) ? $a2[$key] : null;
}

print_r($new);

RESULT

Array
(
    [56] => 
    [60] => aa
)

Or even

$a1 = [56,60];
$a2 = [60 => 'aa',61 => 'bb',62 => 'cc',63 => 'dd'];

$new = [];

foreach ( $a1 as $key )  {
    $new[$key] = $a2[$key] ?? null;
}

print_r($new);

RESULT

Array
(
    [56] => 
    [60] => aa
)