def split_columns(df, separator, new_columns, column_names):
    """
    Split column in data frame into two.

    Args:
        df (pandas table): 
        separator (string): values separator to split
        new_columns (list): names of the new columns
        column_names (string): names of the column to split

    Returns:
        table: new data frame with the column splited into its values
    """
    df[new_columns] = df[column_names].str.split(separator, expand=True)
    return df