def check_index_col(data, index_col):
    """
    check the index column's values are unique.

    Parameters
    ----------
    data : pd.Dataframe
    index_col : str

    Returns
    ----------
    data : pd.Dataframe,
        origin data
    """

    index_col_data = data[index_col]
    if index_col_data.shape[1] == index_col_data.drop_duplicates().shape[1]:
        return data
    else:
        raise ValueError("the index column '{}' values must be unique".format(index_col))