// We can make that with this simple FOREACH loop :
$fruits = array("d" => "lemon", "a" => "orange", "b" => "banana", "c" => "apple");
foreach($fruits as $cls => $vls)
{
$fruits[$cls] = "fruit: ".$vls;
}
Results:
Array
(
[d] => fruit: lemon
[a] => fruit: orange
[b] => fruit: banana
[c] => fruit: apple
)