def get_sub_dataframe(df, measurement_concept_id, unit_concept_id):
    """
    Retrieve subset of the dataframe given a measurement_concept_id and unit_concept_id
    
    :param df: dataframe
    :param measurement_concept_id: measurement_concept_id for which the subset is extracted
    :param unit_concept_id: the unit_concept_id for which the subset is extracted
    :return: a subset of the dataframe
    """
    
    indexes = (df['measurement_concept_id'] == measurement_concept_id) \
        & (df['unit_concept_id'] == unit_concept_id)
    return df[indexes]