def mcycle(return_X_y=True):
    """motorcyle acceleration dataset

    Parameters
    ----------
    return_X_y : bool,
        if True, returns a model-ready tuple of data (X, y)
        otherwise, returns a Pandas DataFrame

    Returns
    -------
    model-ready tuple of data (X, y)
        OR
    Pandas DataFrame

    Notes
    -----
    X contains the times after the impact.
    y contains the acceleration.

    Source:
    https://vincentarelbundock.github.io/Rdatasets/doc/MASS/mcycle.html
    """
    # y is real
    # recommend LinearGAM
    motor = pd.read_csv(PATH + '/mcycle.csv', index_col=0)
    if return_X_y:
        X = motor.times.values
        y = motor.accel
        return _clean_X_y(X, y)
    return motor