[{'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:# Date\n\n# Create Year and Month columns\nrossmann_df[\'Year\']  = rossmann_df[\'Date\'].apply(lambda x: int(str(x)[:4]))\nrossmann_df[\'Month\'] = rossmann_df[\'Date\'].apply(lambda x: int(str(x)[5:7]))\n\ntest_df[\'Year\']  = test_df[\'Date\'].apply(lambda x: int(str(x)[:4]))\ntest_df[\'Month\'] = test_df[\'Date\'].apply(lambda x: int(str(x)[5:7]))\n\n# Assign Date column to Date(Year-Month) instead of (Year-Month-Day)\n# this column will be useful in analysis and visualization\nrossmann_df[\'Date\'] = rossmann_df[\'Date\'].apply(lambda x: (str(x)[:7]))\ntest_df[\'Date\']     = test_df[\'Date\'].apply(lambda x: (str(x)[:7]))\n\n# group by date and get average sales, and precent change\naverage_sales    = rossmann_df.groupby(\'Date\')["Sales"].mean()\npct_change_sales = rossmann_df.groupby(\'Date\')["Sales"].sum().pct_change()\n\nfig, (axis1,axis2) = plt.subplots(2,1,sharex=True,figsize=(15,8))\n\n# plot average sales over time(year-month)\nax1 = average_sales.plot(legend=True,ax=axis1,marker=\'o\',title="Average Sales")\nax1.set_xticks(range(len(average_sales)))\nax1.set_xticklabels(average_sales.index.tolist(), rotation=90)\n\n# plot precent change for sales over time(year-month)\nax2 = pct_change_sales.plot(legend=True,ax=axis2,marker=\'o\',rot=90,colormap="summer",title="Sales Percent Change")\n# ax2.set_xticks(range(len(pct_change_sales)))\n# ax2.set_xticklabels(pct_change_sales.index.tolist(), rotation=90)\''}, {'role': 'assistant', 'content': 'data_preprocessing'}]