Number of positive labels divided by number of labels,
        or zero if there are no labels

def baseline(y_true, y_score=None):
    """
    Number of positive labels divided by number of labels,
        or zero if there are no labels
    """
    if len(y_true) > 0:
        return np.nansum(y_true)/count(y_true, countna=False)
    else:
        return 0.0