This is wrong
echo $output = implode(',', $go);
This will echo the outcome of the assignment of the =
You should try
echo implode(',', $go);
Or this
$output = implode(',', $go);
echo $output;
Or
var_dump($go);
Edit
$array = array();
foreach($ga->getResults() as $result){
$array[] = $result->getVisitors();
}
echo implode($array, ",");