def get_best_so_far(db, datarun_id):
    """
    Get a series representing best-so-far performance for datarun_id.
    """
    # generate a list of the "best so far" score after each classifier was
    # computed (in chronological order)
    classifiers = db.get_classifiers(datarun_id=datarun_id)
    y = []
    for l in classifiers:
        best_so_far = max(y + [l.cv_judgment_metric])
        y.append(best_so_far)
    return y