def combine_first_last_name(df):
    """
    Combine first and last name if df has those columns.
    """
    if 'first_name' in df.columns and 'last_name' in df.columns:
        df['full_name'] = df['first_name'] + ' ' + df['last_name']
        df.drop(['first_name', 'last_name'], axis=1, inplace=True)
    return df