best method to manipulate array keys in PHP

Question

I have an associative array. I need to add ':' to the start of all the keys.
What would be the fastest/simplest way of doing this?
And what would be the most efficient way to do this?

Answer 1

$newarray = array();
foreach($oldarray as $key => $value) $newarray[':' . $key] = $value;

Answer 2

the simplest way would probably be to build a new array:

$newArray = array();
foreach($array as $key => $value)
{
    $newArray[":" . $key] = $value;
}