def standardise_cell_values(pd_df, dict_of_nonstandard_standard):
    """
    Maps non-standard values e.g. "Males" to standard values like "M".
    Mapping is carried out on a column-specific basis.
    """
    df = (pd_df.replace
          (to_replace=dict_of_nonstandard_standard,
          value=None))
    return df