[{'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:mean_revenue_per_city = train[['City_Cluster', 'revenue']].groupby('City_Cluster', as_index=False).mean()\nmean_revenue_per_city.head()\nmean_revenue_per_city['revenue'] = mean_revenue_per_city['revenue'].apply(lambda x: int(x/1e6)) \n\nmean_revenue_per_city\n\nmean_dict = dict(zip(mean_revenue_per_city.City_Cluster, mean_revenue_per_city.revenue))\nmean_dict"}, {'role': 'assistant', 'content': 'data_preprocessing'}]