/**
* @param StackLevel $stack
* @return array
*/
private function groupOperators(StackLevel $stack)
{
$group = array();
foreach ($stack->get() as $item) {
if ($item instanceof StackLevel) {
$group[] = $this->groupOperators($item);
} elseif ($item instanceof StackExpression) {
$group[] = $this->arrangeSet($item);
} else {
throw new QueryParserException("Unexpected value in item of type: " . gettype($item));
}
}
return [$stack->getOperator()->get() => $group];
}