def select_criteria(comparison_data, crit):
    """Extracts not None comparisons of one criteria

    comparison_data: output of fetch_data()
    crit: str, name of criteria

    Returns:
    - list of all ratings for this criteria
        ie list of [contributor_id: int, video_id_1: int, video_id_2: int,
                    criteria: str (crit), score: float, weight: float]
    """
    l_ratings = [
        comp for comp in comparison_data if (comp[3] == crit and comp[4] is not None)
    ]
    return l_ratings