$data['x'] = $this->x->getResults();

$data['y'] = $data['x'];

//some code here to modify $data['y']
//this causes (undesirably) $data['x] to be modified as well

$data['x'] = $this->x->getResults();
   $data['y'] = $data['y'];
   foreach($data['x'] as $key=>$row) {
       $data['y'][$key]->some_attr = clone $row->some_attr;
   }

$data['y'][$key] = clone $row;

$x = 'x';
$y = 'y';
$arr = array(&$x,&$y);
print_r($arr);

echo "<br/>";
$arr2 = $arr;
$arr2[0] = 'zzz';
print_r($arr);
print_r($arr2);

echo "<br/>";
$arr2 = array_flip(array_flip($arr));
$arr2[0] = '123';
print_r($arr);
print_r($arr2);

array_flip()

$data['x'] = array_flip(array_flip($this->x->getResults()));
$data['y'] = $data['x'];

$data['x'] = $this->x->getResults();
$data['y'] = array();
foreach($data['x'] as $key => $obj) {
    $data['y'][$key] = clone $obj;
}

$v=11;
$arr[]=&$v;

$data['x'] = array(
    'a' => 'test',
    'b' => 'glop',
);
$data['y'] = $data['x'];
$data['y'][0] = 'Hello, world!';
var_dump($data['x']); // a => test : no problem with arrays

$data['x'] = (object)array(
    'a' => 'test',
    'b' => 'glop',
);
$data['y'] = $data['x'];
$data['y']->a = 'Hello, world!';
var_dump($data['x']); // a => Hello, world! : objects are by ref

$data['x'] = (object)array(
    'a' => 'test',
    'b' => 'glop',
);
$data['y'] = clone $data['x'];
$data['y']->a = 'Hello, world!';
var_dump($data['x']); // a => test : no ref, because of cloning