def get_feature_values(x: np.ndarray, single_index_feature: bool) -> list:
    """
    Returns a list of unique values of a given feature.

    :param x: The feature column(s).
    :param single_index_feature: Bool representing whether this is a single-column or multiple-column feature (for
                                 example 1-hot encoded and then scaled).
    :return: For a single-column feature, a simple list containing all possible values, in increasing order.
             For a multi-column feature, a list of lists, where each internal list represents a column and the values
             represent the possible values for that column (in increasing order).
    """
    values = []
    if single_index_feature:
        values = np.unique(x).tolist()
    else:
        for column in x.T:
            values.append(np.unique(column).tolist())
    return values

    Returns a list of unique values of a given feature.

    :param x: The feature column(s).
    :param single_index_feature: Bool representing whether this is a single-column or multiple-column feature (for
                                 example 1-hot encoded and then scaled).
    :return: For a single-column feature, a simple list containing all possible values, in increasing order.
             For a multi-column feature, a list of lists, where each internal list represents a column and the values
             represent the possible values for that column (in increasing order).
    
art/utils.py