/**
  * delete all users and users' attributes from recommender
  *
  */
 public function clear(DataApi\Client $client)
 {
     if (!$this->config->isAppend()) {
         $client->deleteUsers();
         $usersAttributes = $client->getUsersAttributes();
         if (isset($usersAttributes['attributes'])) {
             foreach ($usersAttributes['attributes'] as $attribute) {
                 $client->deleteUsersAttribute($attribute['name']);
             }
         }
     }
     return $this;
 }