'Online evaluation for recommendation prediction
Parameters
metrics: [None|\'rmse\'|\'f1score\'|\'precision\'|\'recall\'|\'nmae\'|\'mae\']
If metrics is None, all metrics available will be evaluated.
Otherwise it will return the specified metric evaluated.
Returns
Returns scores representing how well the recommender estimated the
preferences match real values.'

def evaluate_online(self, metrics=None, **kwargs):

    raise NotImplementedError('cannot    instantiate    Abstract    Base    Class')
