def get_demo_data(df, demo_data="my travel map"):
    """
    This function gets the three demo datasets.

    Parameters
    ---
    dataframe : pandans.DataFrame
        This is the input dataframe named "demo_fake_data".

    demo_data: {"my travel map", "life log", "starbuck"}, default "my travel map".
        my travel map: This is the fake dataset for a travel foot print log including 4 cities in NY: New York -> Seattle -> Los Angela -> Miami.
        life log: This is the fake dataset contains the daily active routine of a Columbia nerd.
        starbuck: This is the fake dataset contains the starbucks income changed by date around New Haven city and neighorhoods.

    Returns
    ---
    Relative dataframes.

    Example
    ---
    travel = pv.get_demo_data(df, "my travel map")
    life = pv.get_demo_data(df, "life log")
    starb = pv.get_demo_data(df, "starbuck")

    >> travel.columns
    Index(['unique_id', 'spot_name', 'street', 'city', 'state', 'country',
       'interest_value', 'date', 'symbol'],
      dtype='object')

    """
    if demo_data == "my travel map":
        df = df.iloc[
            0:4,
        ]
    elif demo_data == "life log":
        df = df.iloc[
            4:7,
        ]
    elif demo_data == "starbuck":
        df = df.iloc[
            7:,
        ]
    return df