Return key values from first array whose key is in second array

You can do this in one line in PHP, using array_flip to swap the keys and values of the second array, and then array_intersect_key to merge the two arrays on matching keys:

$colldata=array("bench-press-rod"=>'',"adidas-classic-backpack"=>'93549559913',"adidas-classic-backpack-legend-ink-multicolour"=>'',"puma-suede-classic-regal"=>'93549920361,93549723753');
$colldata2=array(0 => 'bench-press-rod',1 => 'adidas-classic-backpack');

print_r(array_intersect_key($colldata, array_flip($colldata2)));

Output:

Array
(
    [bench-press-rod] => 
    [adidas-classic-backpack] => 93549559913
)

Demo on 3v4l.org

About the simplest I can come up with is to loop through the second array and add the matching key from the first array into the output. If the item isn't present then it puts Not found in the output...

$output = [];
foreach ( $colldata2 as $item ) {
    $output[$item] = $colldata[$item] ?? 'Not found';
}
print_r($output);

gives..

Array
(
    [bench-press-rod] => 
    [adidas-classic-backpack] => 93549559913
)

Check this.

$colldata=array("bench-press-rod"=>'',"adidas-classic-backpack"=>'93549559913',"adidas-classic-backpack-legend-ink-multicolour"=>'',"puma-suede-classic-regal"=>'93549920361,93549723753');
$colldata2=array(0 => 'bench-press-rod',1 => 'adidas-classic-backpack');

$result = [];
foreach ($colldata2 as $key => $value) {
    if (array_key_exists($value, $colldata)) {
        array_push($result,$colldata[$value]);
    }            
}
echo '<pre/>';
print_r($result);