def get_cpgs_orig_methylated(df, cells_to_use):
    """
    Get a list of cpg which where methylated to begin with using a specific set of cells
    :param df: The df to work on
    :type df: pd.DataFrame
    :param cells_to_use: A list of cells to use, should match the rows names of the df
    :return: The indexes of CpG to use
    """
    df_orig = df.filter(items=cells_to_use, axis=0)
    mean_values = df_orig.mean()
    return mean_values