[{'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:#Standardizing numerical variables\nfrom sklearn.preprocessing import StandardScaler\ncols = ['temp','atemp','humidity', 'windspeed', 'Month_sin', 'Month_cos', 'Hour_sin', 'Hour_cos', 'DayOfWeek_sin','DayOfWeek_cos']\nfeatures = data[cols]\n\n#Standard Scaler\nscaler = StandardScaler().fit(features.values)\ndata[cols] = scaler.transform(features.values)"}, {'role': 'assistant', 'content': 'data_preprocessing'}]