[{'role': 'system', 'content': "You are an expert in machine learning and your task is to classify code snippets into one of the following categories: ['helper_functions', 'load_data', 'data_exploration', 'data_preprocessing', 'evaluation', 'modelling', 'prediction', 'result_visualization', 'save_results', 'comment_only']."}, {'role': 'user', 'content': "Identify the single most appropriate category to which the provided code belongs. Provide your response as a single category label without any additional information, commentary, or personal opinions.\\nPython Code:# competition open time (in months)<br>df['CompetitionOpen'] = 12 * (df.Year - df.CompetitionOpenSinceYear) + \\\\<br>        (df.Month - df.CompetitionOpenSinceMonth)<br>    <br># Promo open time<br>df['PromoOpen'] = 12 * (df.Year - df.Promo2SinceYear) + \\\\<br>        (df.WeekOfYear - df.Promo2SinceWeek) / 4.0<br><br>df = pd.get_dummies(df, columns=['DayOfWeek', 'StoreType', 'Assortment','PromoInterval'], dummy_na=True)"}, {'role': 'assistant', 'content': 'data_preprocessing'}]